15(4), 301-309 Tap chi CAC KHOA HOC VE TRAI B A T
\ / D A C DIEM PHAN HOA MU'A LC5N VUNG VEN BIEN TRUNG BO TlT THANH HOA DEN
KHANH HOA TREN CO SCJ PHAN TICH HINH THAI DIA HINH
NGUYEN KHANH VAN, TONG PHUC TUAN, VUONG VAN VU, NGUYEN MANH HA
E-mail, [email protected]
Vi^n Dia ly, Vi^n Hdn ldm Khoa hgc vd Cong nghi Viet Nam Ngay nhan bai: 10-9-2013
1, Md dau
Nhirng nira gin day dii ven bien Trung Bg Vift Nam lien lyc phil hung chiu rat nhieu thien lai do thdi tiet kht hfu bat lgi, trong dd cd thifn lai do raua Idn. Mua Idn sinh lu lyt, lu ing, lu quel lam s?t Id dudng sa, bd sdng, gay ngap lyt nha cfta, ruf ng, vudn, hoa miu cua ngudi dan, buy hoai cic cfing trinh cfing cgn§, lira bien dfii mdi trudng ty nhifn, mfii trudng song, inh hudng den cac boat dfng kinh te cfta ci mgt khu vyc rfng Idn.
Nghien cuu diiu kifn hoin luu khi quyen vi eic tic nhan giy mua Idn d vung ven bien Mifn Trung di dugc df cap den trong mft so bai bio [2, 4-6]. Hinh thf thdi tiit (HTTT) gay mua Idn d day la bio, ip thap nhift ddi (ATND), hfi ty nhift ddi (HTND), hfi ty kinh hudng (HTKH), khfing khi lanh (KKL),... vi ho^t dgng dfing thdi hoic gfli tiep nhau cua tfi hgp hai hoic ba HTTT dd,
Tuy nhifn, nghien cftu sy cgng hudng cua hinh Uiii dia hinh (HTDH) khu vyc vdi nhftng tac nhan gay mua nfu ttfn cho din nay chi mdi dugc di cap den trfn nhftng khu vyc cy the (bic deo Ngang vi nam dfo Ngang) [9]. Dgc theo bd bifn Miin Trung, vdi chi dg mua "thu dfing", xuit hifn lien tyc nhftng dgt mua Idn, rat Idn va vai ttd cua dia the dai Trudng San (d phia tiy), sy ehuyen hudng dudng bd biin (d phia ddng), cung nhu vi thf kha d$c bift cua cie nhanh nui chay ra sat bien (deo Ngang, deo Hii Vin, dfo Cu Mfing, deo Ci,...) eho den nay vSn edn Ii van de rat ly^ thft cin dugc nghien ciru tiep.
Bai bio nay tap tnmg phan tich sy khac bift cua dac diem HTDH, su chuyen hudng dudng bd (so vdi hudng xam nhap cua hoan luu gio miia Dfing Bac - raft trong nhung tic nhan chinh hinh thanh nen che dg mua "thu dong" dac Ihii ciia linh thfl), sy hifn difn cua cac deo Ngang, Hai Van va deo Ci - xem do nhu nhftng lac nhan quan trgng dan tdi su phan hda cac dgt mua Idn (lifn quan den hoat dfng ciia cac HTTT KKL) d dai ven bien tu Thanh Hda din Khanh Hoa, die bift li sy phin hda ve mua Idn giua cac khu vyc trudc va sau cac deo.
2. Vung Dghien cftu, dft lifu va phuang phip nghien cftu
2.1. Vdng nghien cu-u
Vimg nghifn cftu la dii ven bien thufc Trung Bf Vift Nam bao gdm 12 tinh va thanh pho keo dai tu Thanh Hoa den Khanh Hda, ed difn tich ty nhien la 95.956,48 km= (chiim 28,93% difn tich ca nudc), dan sfl nara 2011 la 17657,2 nghin ngudi (chiim 20,1% dan sd ca nudc). Day la khu vyc nfli tiing nhiiu thien tai mua Idn, bao lu, dieu kifn khi hau khic nghift, la khu vyc cd dieu kifn kmh te - xa hgi khd khan, khi nang phong chdng thifn tai thip kem ban cic khu vyc khac. Diem ndi bat cua dia hinh dai ven bifn tu Thanh Hda den Khanh Hda li lanh thfl keo dai, h?p (nai rfng nhat khoing 200 km, nai h?p nhit chua tdi 50 km), thong tri bdi cic diy, khoi nfti thugc dai Trudng San va cao nguyen Lam Vien d phia tay, phia dong Ii bifn, dia hinh dflc va nghifng tft tay sang dfing la chft yeu.
301
Khdng nhu nhirng viin^ khi hau khac d nudc ta (Tay Bic, Dfing Bac, Ddng bing Bic Bg, Tay Nguyen, Nam Bg) cd chf df raua miia he, chu yfu do gid mua Tay Nam, vftng ven bifn Mien Trung (ttong dd cd khu vyc nghifn cuu) cd chf dg mua do gio miia Dfing Bac chi phdi la chinh [1]. Do su ket hgp gifta cac tic nhan gay raua va dia hinh, dia the khu vyc, mfta mua d Mifn Trung thudng bao gflm 2 thdi ky: mua tieu man (tft giua thing V den thing VI) vi raua chinh vy (tft thing VIII den thing XI, XII). Trong mua mua chang nhung tflng lugng mua cao, so ngiy mua nhieu ma cdn tfp trung rit nhieu ngay mua Idn (> 50 mm/ngay) vi mua rat Idn (> 100 mm/ngiy) thanh timg dgt.
Phan tich sa bg dac diem HTDH dii ven bien tft Thanh Hda den Khanh Hda cho thay tft bac vao Nam qua han 8 vy dg dia ly, vung nghien cftu co thf phan chia bdi cic nhinh nui chay ngang ra sit biin thanh 4 khu vyc Idn. Neu quan nifm nhftng khic biet dac thii rieng cua dieu kifn dia hinh d tftng khu vuc la nhung tic nhan quan trgng din den sy cgng hudng cua HTDH vdi cac HTTT giy raua Idn thi cac khu vyc niy lan lugt li: Khu vyc 1 (KVl) tu Thanh Hoa dfn bic deo Ngang; Khu vyc 2 (KV2) tft nam deo Ngang dfn bac deo Hii Van;
Khu vyc 3 (KV3) tft nam deo Hai Van den bic deo Ca vi khu vuc 4 (KV4) tu nam deo Ci den hft dia phin tinh Khinh Hda.
2.2. Cas&dirlifu vd phuang phdp nghien cuu 2.2.1 Cas&daiiiu
Nghien cftu sy phan hoi mua Idn tren ca sd phan tich HTDH cac khu vyc d dii ven bien tft Thanh Hda den Khanh Hda di sft dyng:
- Cic du lifu trac lugng hinh thii dia hinh vung nghien cuu ttfn ban dfi dia hinh, ty If 1:250.000:
hudng son van, df cao trung binh cua dudng dinh, df dai cua cac diy nui, dg chia cat sau, dac difm dia hinh, hudng dudng bd cic khu vyc ven bien (nai tifp xiic dau tien eua cac khoi khi ndng am tft bien vao).
- Cic sd Iifu khi hau bao gora sd lifu thdng kf phan loai tan suit hoat dgng cua cac HTTT giy raua Idn ttfn khfing gian tft Thanh Hda dfn Khinh Hda, thdi ky 1987-2006 va cac sd lifu lugng mua ngay (tich luy 24 gid) cua cie ttam khi tugng, difm do mua tren toin vung nghien cuu [7, 8].
2.2.2. Cdc phuang phdp nghiin cuu Nghifn cftu sy phan hoa cua raua Idn vdi
HTDH cic khu vyc ven biin bii bao da sft dyng cac phuang phip sau:
- Phuang phap thing kf phan lo^i khi tugng synop: phan tich va phan loai cic HTTT va td hgp cac HTTT gay mua Idn tten cac ban dd synop;
Thfing kf tin suit hoat dgng cac HTTT gay mua Idn va to hgp cua chung.
- Phuong phip thfing ke khi hau: phin tich dien bien, thdi gian keo dii cua cac dgt mua Idn, xac dinh pham vi khong gian inh hudng cfta cic dgt mua Idn.
- Phuang phap phan tich hinh thii dia hinh:
nghien cim dinh tinh (md ta dien mao) va dinh lugng (do dac, phan tich cac thdng sd trac lugng - hinh thai) dia hinh vi HTDH cd y nghia quan ttgng dfli vdi sy phan bd lai vat chat va ning lugng ty nhien (ttong do cd ngudn nang lugng cia mua - mua Idn) trfn bf mat Trai dat.
- Phuang phap phan loai dia ly - hinh thii: phan loai dia ly - HTDH cac khu vyc vdi nhftng dac diem son van, hudng sudn, thf nui, hudng dudng bd bien,... ttong mdi tuong tic vdi hudng chuyen dflng cua eac HTTT gay raua Idn, nhira xac dinh cac khu vyc cd tiim ning mua Idn va mua rit Idn.
3. Ket qua nghien ciru va thao luan
3.1. Bgc diem HTDH vd tiem ndng sinh mua l&n
& Trung Bg
De lam sang td sy phan hoa cfta HTDH dfli vdi mua Idn vung ven bien tft Thanh Hda din Khanh Hda trudc tifn chftng tdi nghien cftu, phin tich hai nhom yeu tfl sau:
- Nhdm dia hinh cau true cd inh hudng Idn den sy hinh thinh cic khu vyc raua Idn, bao gom hudng son vin (dg cao dia hinh, hudng, tinh lifn tyc cua cic day nui, dg cao trung binh dudng phan thuy) va die difm hinh thai cic day mii chinh.
- Nhdm dja hinh mat dfm cd nhftng anh hudng nhat dinh dfii vdi sy tuong tie khdi khi - dia hinh, bao gfim muc dg chia cat sau, chia cit ngang, hinh thii cac Iuu vyc sdng, hinh thii cac kifu dfing bing va hudng dudng bd bien.
Hu^ng san vin: dii Trudng Son vdi hudng son van thdng trj la TB-DN, hinh thinh nen bftc tudng chan d phia lay. Mft sfi nai, trudc mft dii nfti cao d phia tay la mft hoic hai dai nui thap han d phia gan bifn, dien hinh Ii d khu vyc Ha Tinh.
N^oii hudng thing tri TB-DN cua day nui Idn, mgt so nai ciing phat triin cac day nui chay ngang ra bifn nhu Hoinh San va Bach Mi, Deo Ci va mft so deo thip han khae. Chinh nhftng dSy nui niy kft hgp vdi dai nui chmh (Trudng Son) cd hudng TB-DN d Bic Trung Bg, hudng B-N d Nam Trung Bg va chuyfn sang dang gin nhu khdi tang
d Khanh Hda da tao nen nhiing "bay mua" quan ttgng cua viing nghien CLTU.
OQ cao trur>g binh ciia
Hudng son van, do cao trung binh cua dudng dinh, df dai ciia cac day nfti duoc thdng ke tbeo 4 cip do: >1300m; 800-I300m; 400-800m; dudi 400m va ttinh bay d bdng I. hinh 1.
B i n g 1 . Chieu d i i (Itm) vk ty I f cac d i w n g chia ntr<yc cua cac dai niii chinh
% ldng chieu dai Ouiing chia r\u6c {d cdc O^c diem dirdrtg cFiia nu<ic
auOng chia ntn»c (m) T6ng si dirimg T5ng chilu dai (km) Chi4u dai trung binh (km) cap do cao) so vii'i chifeu dai long cgng
>1300 S0O-13DD 400-600
<400 TAng cOng
1.155,0 i.s2i.e 1.480.3 766,6 5.243.7 ' Ngu6n: Bao cao chuySn d f cSc de tSi [7] va [8)
Kft qua thfing ke mft sd dac di6m son van cho ta nhung nh|n xet ban dau nhu sau:
Cac dii nui cao nhit (> 1300m) tuy cd tdng sd dudng chia nudc it nhat nhung lai ed chifu dai trung binh Idn nhat (19,6km), dieu dd cho thay he thing nfti cao nay khi lifn tyc va dfi sf. Tiep theo, nhdm cic dai nui cd d$ cao trung binh 800-I300m vfta cd tflng sd dudng, vfta c6 tflng chifu dai cac dudng diu rit cao (154 dudng va 1.821,8km), Cac dai nut cd dg cao trong khoing 400-SOOra cung co sd lugng dudng Idn - 147 dudng. Nhin chung hai nhdm nfti nay (800-1300ra vi 400-800ra) dfu cd sd dudng nhieu nhit (xip xi 150 dudng ddi vdi mfli cap), vugt trgi Ifn hin so vdi cic nhdm cdn lai, Diiu niy cd ^ nghia rit quan trgng dfli vdi sy hinh thanh cic khu vyc mua dja hinh, cac nhdm niii cd dg cao Wong ddi ding kf tren da "ngin chin"
chuyin dfng eiia cac khfli khi va eic tic nhan gay mua (chft yfu la tft bien vao), lam gia ting chuyen dgng thing d bfn phia sudn ddn gid, gia tang lugng mua,...
- Die difm hmh thai cac day nui chinh: sau hudng son vin, die difm hinh thai cic diy nui chinh cung ddng vai trd cgng hudng kha quan trgng trong sy hinh thinh mua Idn.
Khdi nui chinh Trudng San, keo dai theo hudng TB-DN ed df cao tuong dfii tren 1000m, thudng bao gim mgt so dii niii song song (df rfng trung binh 10-20km) va cac thung lung h?p gifta nui (df rfng trung binh 5-10km), df die sudn cua cic dai nui niy trong khoing 25-30°, mgt sfl khu
vuc niii da vol cdn co do ddc Idn han, hoac dung dung, dien hinh nhu khu vyc Phong Nha-Ke Bang.
- Mue dg chia cat cua dia hinh: chia cit sau (the hifn muc dg map md eiia be mat dia hinh) va chia cat ngang (the hien mftc dg day hoac thua cua mang ludi sflng sufli) d chung myc nhat dinh the hien dg nham, vai trd ma sat ciia mat dem, gdp phan lam ling hoac giam cac chuyen dgng thing, nhieu gay mua ciia cac khoi khi ndng va am.
Dg phan cit sau va chia cit ngang cd sy phan hda rd rfl tren viing ven bien Trung Bf, ca theo phuong tft bic vao nam, ca theo chifu tu lay sang dfing. Tren co sd phan lich df phan cat sau trung binh ciia 4 khu vyc nghien cim, vdi gia trj d viing mii 300-400m/km^ den 600-700ni/km^ {bang 2) co thi thiy vc phia nam vung nghien cuu, df phan cat sau chang nliung Idn han so vdi phia bac ma cdn cd nhung dgt bien dang kc cd kha nang chi phdi lao nfn cac bay mua dia hinh,
- Hinh thai be mat: doi vdi cac khu vyc tiep giap vdi bien, cac kieu dia hinh dang dai cdn cat ven bien (difn hinh cho dai ven bien Trung Bf) vdi nhftng dg cao, dg rfng khac nhau cung la nhftng tic nhan ding ke cua yfu td mat dfm tham gia vao qua ttinh gia ting cac chuyen dgng Ihang, tao nen sy cfng hudng cua dia hinh vdi mua Idn. Cy the, ddi vdl KVl cac luu vyc sdng va dfing bing md rgng sang phia tay, dai cfln cat vcn bien hep vi thap. KV2 dai cfln cit phit trien rgng va cao hon ca so vdi cic khu vyc khac, trong Idii dd luu vyc sflng thu h^p vi ddc. KV3 dai cdn cat giira di dang ke,
Iuu vyc sflng Thu Bdn md rdng ve phia nam vdi da tao nfn biy mua dia hinh nfii tieng Tri My.
dia ban Tra My (Quang Nam) cd vi tri kha die bift Sang KV4 hinh thai bi mat nfii trgi d day la cac - phia tay la Nam Trudng Son liin mgt dii, phia khfii va day nui an sat ra bifn lam cho cic thung nam va phia dfing li mgt sfi day nui thip han, tit ca Iiing sdng rat ngan va die (bdng 2).
Hinh 1 Sc do hu«ng scm van dai ven \nkn tCr Ttianh H6a d i n KMnh H6a
• Ngufin Bao cao chuyen dfi cac d4 tdi [7] vd [8J
M n g 2 . Nhifng phan hoa chtnh cOa di^u k i f n HTDH gi&a 4 khu vifc chinh cua v u n g nghien ciru D$c diSm cac d3y Cao hon d phia bSc vung Thip dfin vfi phia nam vUng
nui va klioi nCri phia , BTB TSy
Vi Iri, dfl cao cua,'- DayHo^ijtiponchgy cSc nhanh nui chgy ngang' ra bien. cao trung ra sat Biln Oang binh khoang 600-600 m Ddc difim ph'an cSi Vcing nui PCS: 300- sau (PCS) cua d]a 400m/km^
^'"^ Vung dfii. niJi s6t (r^ng 20- 30km) PCS: 100- 200m/km^
VCing dfing bing ven bien PCS:10-50m/km=
Cac LVS rOng 16n v l phia lay, c6 LVS sang cd lanti tho VLing Tdy Bic, CHDCND Lao.
T^p Irung nhieu khfii cao & D^ng khfii cao Chilm inj phia bSc vi giam chifiu the cao dang ke o phia nam
Day Vgng Phu - Tam Day Niii Chua Ninh Thujn Phong, kha thing, hiri^ng g i n nhir dang khU b E)N k6o dai DB-TN. cao trung Khanh Hba, cao trung binh bmh 800-1200m. 1200-2000m Viing niii Quang Nam PCS 0|a hinh nCii chilm ifu thi
\<3n. dgt toi 500-600m/km', Idn hon hin so v*i cdc khu khu VI/C nui c6n lai c6 d§ vi^: khde. DO PCS tnjng PCS 300-400m. binh 300-«IOm/km^ cd bi$t Trfin t)fi mat dong bdng c6 ^^ •*' 600-700m/km'.
mfit sfi khoi nui, nui s6L Ddy Bach Md chgy ngang ra
sdt bilrt. cao tnjng binh khodng BOO-IOOOm, hui^ng phin iam v l phia DB VCing nCii (son nguydn xen kS thung IQng khodt sdu, hdm VI/C) PCS: 300-400 m/km' VCing dfii h?p hon, nhirng PCSd?t150-250m/km^
Dfing bdrtg ven biln h;p (10-15km)vdc6 cdc dfii.
niJi s6L
Cdc LVS bKmg dfii h«p. LVS Thu Bon Ion nhll, ch Chu y l u Id LVS Cdi (Nha ngin. die phin Idm ndm trpn hinh thdi biln dfii manh Trang) Cdc LVS r l l ngin.
trdn Idnh thfi Vi|t Nam, theo ^ a hinh. Cac liru virc dfic, tap trung nirdv r l l khac thing, h^p. ngdn, nhanh vd It bfii tich Hinh thdi cdc kilu
dfing bdng vd cac cfin cat khu vyc ven biln.
Hu*ng du'fi'ng bfr (theo y nghTa phuong tilp c$n ci^a l^ic dia dAi vdi hu^ng gifi gdy mu:
chi3 dgo)
Cac kilu dfing tidng rfing d'ThanhH6a, Ngh#An, Dai cfin cat ven biln cao 5-10m.
Dudng bd biln phia a6ng chgy chQ ylu theo hudng
Kilu ding bing hep (10- Dfing bing Qudng Nam c6 Di$n tich dfing bing hiu 20km) d Binh Tn Thidn, ddi di^n tich ddng k l . nh&ng nhir khOng cd, chu ylu cfin cdt cao 10-50m va mQI noi khac r l l h^p. Cdc dfing phat tnin cdc vung vinh vd ddi dim pha ven biln Idn bdng ngufin gfic biln (cao bli tich ven bd nhll ca rtuTi'C (ddi 70km, 10-20m) c6 y nghia dang k l cdc dyn cdt phdt Inin rOng - 10km. sdu - 10m). cho sdn/xuat nong nghidp [(^Ong lidn tgc, diln hinh d
Cfin cdt it phdt tnin hon so khu vi/c bdn oao Hdn vdl KV2 Gfim. Dfic Lit.
Dudng bd biln phIa ddng Dudng bd biln chuyin lir Dudng tid biln chu ylu cfi chil ylu theo hu^ng tdy bic Tdy Bic (phia bic KV3) hu^ng Bic Nam. Bd biln - dflng nam sang Bic Nam (phia nam chu yiu Id dd gfic vd cd
KV3J, nhilu vOng winh.
- Hudng dudng bd: vai tr6 eiia duong bd bien trong s\i hinh thanh mua dja hinh tir lau di dugc de c^p den trong rit nhieu nghien cuu, die bift li nghifn cijru ve ca chi boat dgng ciia gid mua Dfing Nam A [10, II]. 6 Vift Nam dac bift lad ven bifn Mien Trung vdi su xuat hifn ctia kieu miia mua
"thu dong" (khfing diin hinh cho viing nhift ddi), dudng bd bifn, dac bift la khi dudng bd cd hudng vufing gde vdi chuyfn dfng ctia cic khii khfing khi giiu im tir biin Ddng tran vao cd tic d\mg cgng hudng vdi diiu kifn dja hinh khu vyc Iim gia ting ehuyen dgng thing gay nfn cac khu vvc co mua dja hinh {})dng 2) vk hf qui cuii eung Ii s\r djch chuyen ctia miia mua dan sang cuii thu dau dfing d ven biin Trung Bg [4].
3.2. Slf ph&n hoa vi HTDH vd mua Idn giira cdc khu v^ & ddi ven bien tir Thanh Hda den Khdnh Hda 3.2.1. Phdn hoa HTDH giOa cdc khu vifC
NhOng thing ke, phin tich sv khic bift vf d$c diim HTDH tren 4 khu v\rc viing nghifn cdu dugc
trinh bay tren bdng 2.
Tom lai tren mft khfing gian khoing tren 8 vl dg dja Iy, cac khu vgc co nhOng khac bift chinh vi HTDH sau:
- O KV 1 cac bg phan thufc day niii Trudng Son eao hon d KV2 va cd tinh lien mach hon. Chuyen sang KV3 va KV4 tinh chit tuyin din bj thay thi bing heh chit khdi eiia cac dai nui.
- d KVl vung doi mii cd phan eit sau nhd hon so vdi KV2. Cac KV3 va KV4, difn tich dfii hiu nhu tieu bifn, chi cdn cd cac khoi vi nhanh niii vdi muc df phan cit sau cao.
- 0 KVl cic Iuu vgc song Idn va md rgng han, trong khi d KV2 cac luu vgc sfing h?p, ngin vi doc.
Sang dfn KV3, KV4 cic song hiu het cd dang cit se long, nhifu noi diy sfing tro If da gfic.
- KVl cd dong bing ven bien rfng ban so vdi KV2. Cic dfing bing d KV3 va KV4, ngoai dong bing (Juing Nam thi dfu cd difn tich rit nh6.
305
- Nhung con cat ven bien cd anh hudng Idn nhit tdi chf dg thiiy van d KV2 va tilp den la KV 1 nhung gia tri tifm nang phat trifn KT-XH lai eao han bin d K V 4 v i K V 3 .
- Hudng dudng bd chii dao ciia KVl la B-N, ciia KV2 la TB-DN, ciia KV3 la TB-DN (d phia bic) va B-N (d phia nam), cua KV4 la hudng B-N.
3.2.2. Phdn hoa cda cdc HTTT mua l&n vd tdn sudt mua l&n co lien quan den hogt dgng cua KKL
Mua Idn va rat Idn tren dien rgng la hf q u i tuang t i c giua hoat dgng cua cac HTTT gay mua CO tinh hf thong vdi dieu kien dia hinh tung khu
vuc. Cac khu vgc dugc phan chia nay mgt mat phai
"du rgng" df khfing lam " m d nhat" tinh hf thfing ciia b i n than hifn.tugng m u a Ion, mat khac ciing
"khong thf qua hep", dii de "lam sang t o " dirge sg khac bift ciia t i c nhan HTDH cgng hudng vdi cac HTTT gay nen mua Idn tren tung khu vuc.
Theo cac k i t q u i nghifn cuu ve mua Idn dS dugc tiin hanh [4, 6] vdi c i c tieu chi de x i c djnh mua Idn v i mua rit Idn' dugc df xuat trong [7], ket qua p h i n loai v i thong kf sfi dgt mua Idn va tan suit xuat hien mua Idn ciia tung loai HTTT trfn 4 khu vuc vung nghien cuu dugc the hien trong bdng 3.
Bang 3. T h o n g ke s 6 d g t mu'a \an va t a n s u a t x u i t h i f n eac HTTT g i y mipa lo-n d 4 k h u v i f c v u n g nghien c d u , giai doan 1987-2006
Hinh t h i thdi tilt 1. Bao hoac ATND 2 HTNO 3 KKL
4. Bdo (hoac ATNO) vd KKL 5 HTND vd Bao (hojc ATND) 6 HTND vd KKL
7. Rdnh thap va gid SE; gid NE; gid SW; NhiSu dfing trong dcri gid Ddng trdn cao Tfing sfi
17.9 29.8 10.4
11.7 15,3 37,0
20,9 18,0 8,8 100,0 100.0 100,0
* Ngu6n: Bao cdo chuyen de cdc de tai [7] va [81 Phan tich sfi lifu thdng ke bdng 3 cho t h i y nhdng khac bift nhu sau:
Tan so v i t i n suat x u i t h i f n c u a cac H T T T g a y mu'a Idn:
- V i cac HTTT giy mua Idn: tren Ianh thfi nghifn cuu tfing cfng cd 7 loai HTTT gay mua Idn, trong do chi rifng d K V l , qua 20 nam chua quan sat thiy dgt mua Idn nao lifn quan den HTTT s6 4: to hgp thdi tiit Bao (hoac ATND) v i KKL.
- V i tong sfi dgt mua Idn: trfn c i e khu vgc tdng sfi dgt mua Idn lin lugt la: K V l : 67 dgt; KV2: 111 dgt (gip 1,66 lin so vdi KVl); KV3: 57 dgt (chiem 0,85 sfi lin so vdi KVl) v i KV4: 34 dgt (chiim 0,51 sfi lin so vdi KVl). Ndi each khac, cang vf phia nam tdng sfi dgt mua Idn cing it di: tinh trung binh nfu
nhu hang n i m d KVl cd khoang 3,4 dgt mua Idn/nim tbi d cac idiu v\ic khac Ian lugt la KV2: 5,6 dgt/nam. KV3: 2,85 dgt/nim va KV3:1,7 dgt/nim.
- Ve tan suit xuat hifn cao nhat eua cie HTTT gay mua Idn trfn tirng khu vgc: doi vdi K V l do l i HTND, chifm tdi 29,8% l i n g s6 dgt. 0 KV2 Ii KKL, chiim 37,0%. 6 KV3 la HTND v i KKL, chiim tdi 24,6% va d KV4 lai la KKL, chiim tdi 38,2%. Nhin chimg, % khu vgc cd t i n suit HTTT xuat hifn cao dfu cd lifn quan den KKL hoic tfi hgp ciia KKL vdi cic HTTT khic.
- Ding luu y c6 HTTT sfl 7 (XT hoac RT v i gio SE; HTKH: Dai thap, vimg thip phia tay...) chiim tin suit kha cao d KVl (20,9%), KV2 (18,0%) nhung Iai cd tin suit khflng cao (8,8%) d KV3 v i KV4.
'Mua Idn: lui^ng mua->SO[nni/ngiy, keo dai tir 2 ngay trd 16n, difn mua chiem > S0% s i tram trong khu vuc;
Mua rdt Idn: lugng mua > I OOnun/ngay, keo dai tit 2 ngiy trd len, difn mua chtem > 50% s i tram trong khu vgc.
306
Nghien cuu mua Idn va vai tro cua HTDH tuong tic vdi mua Idn li mgt van df phuc tap, trong Iiic nhtrng du hfu phan tich chi tiit con ban chi, chiing toi Iga chgn nhimg loai HTTT (dugc xem Ii) ed hudng chuyfn dgng ciia cac tic nhan gay mua tuong dfli ro rang, do la cic HTTT sfi 3: KKL, sfi 4: KKL vdi BK) (hoac ATND), s5 6: KKL vdi HTND va tiin hinh phan tich thanh 2 trudng hgp rifng trudc khi tflng hgp I^i, cyi thf nhu sau:
Mira I d n d o hogt d g n g d o n t h u ^ c u a K K L sau c i c front Ignh:
Cic dgt xim nhap KKL theo hudng DB-TN (HTTI sfi 3), vdi sir tiem in eua eic tic nhan gay mua ben trong be mat front lanh Ii nguyen nhan quan trgng gay mua vi mua Idn d cie khu vue ven bien viing nghien cuu: Co 7 dgt mua Idn do KKL (-10,4% tfing sfi dgt) d KVl; 41 dgt (^36,9%) d KV2; 11 dgt (-19,3%) d KV3 va 13 dgt (-38,2%) d KV4 (bang 4). Cd thi thiy KV2 va KV4 la nhiing khu vgc eo tan suit mua Idn lien quan den KKL dan thuin cao vugt trgi, d?it 36,9% va 38,2%
tfing sfi dgt mua Idn tuang iing trfn timg khu vue.
Bang 4. S6 d g ^ mu'a I d n va tan suat x u i t h i f n cac HTTT m i f a I d n c 6 lien quan den ho ^ t d f n g ctja KKL g 4 khu VIFC v u n g nghien c i r u , giai doan 1987 - 2006
Hinh t h i Uidi t i l t Tfing s l
KKL (HTTT sfi 3)
Tfi hp'p KKL vdi cdo HTTT khde (s6 4 + sfi 6) Tfing h(7p cdc HTTT cd liSn quan din KKL (sfi 3-t-s64 + s66)
Cdc HTTT mtf a Idn cfin lai
100,0 100.0 36,9 19,3
9,0 4S,G
Mu'a Idn d o to h g p K K L va c a c H T T T k h i c :
Cac dgt xam nhip KKL theo hudng TB-DN d phia bic (vdi sg tiim in cua cac tic nhan gay mua ben trong bf mit front Ianh) ket hgp vdi vai tro hgi ty cie khfli khfing khi trong bio, ATND hoic HTND (trong HTTT so 4 va sfi 6) la nguyen nhin gay nen 1 dgt mua Idn (-1,5%) d KVl; 10 dgt mua Idn (-9,0%) d KV2; 26 dgt mua Idn (-45,6%) d KV3 va 11 dgt mua Idn (-32,4%) d KV4.
Tong h g p m y a Idn d o c i c H T T T c d iien quan d e n KKL:
Thing ke ting si dgt mua Idn va tin suit xuat hifn eie HTTT mua Idn co lien quan dfn yiu tfl KKL cho thiy: trong cung mgt thai ky 1987-2006, niu nhu d KVl mua Idn cfl lien quan din KKL chi chiim 11,9% ting sfl dgt, thi d KV2 ty trgng nay la 45,9%, vi d KV3, KV4 chiing lin lugt la 64,9% va 70,6%.
Difu niy cho thay trong khi ting si dgt mua Idn co xu thf ting din tir KVl den KV2, giam tir KV2 qua KV3 din KV4 thi vai tro cfng hudng ciia cae dgt KKL, tfi hgp KKL vi bSo (hoic ATND) hay KKL vdi HTND lai chifm mft ty trgng ngay cang ting:
11.9% d KVl; 45,9% d KV2; 64,9% d KV3 va 70,6% dKV4.
Phii ching sg khic bift rd net vf djcdifm HTDH (hudng son vin, djc diem htnh thii nhthig diy niii chinh,...), hudng dudng bd bifn {bang 2) trong sg
ftiong tic vdi hudng chuyen dich ciia KKL la nguyen nhan quan trgng, lam tang ty trgng eiia so dgt mua Idn lien quan din KKL d 3 khu vgc phia nam viing nghien ciru?!.
4. Kit luuii
Sg phin hoi cua mua Idn va dieu kifn HTDH la mfl vin df phiic tap. Mua Idn va rat Idn la nhiing hifn mgng thdi tiit mang tinh hf thong, khi xuit hifn d viing ven bien Trung Bf, thdi tiet die bift nay lai dugc cfng hudng them bdi vai tro phan dj vita CO tinh hf thong (cac hf thong nui) vira cfl tinh kha cyc bf, dja phuang (cac diy niii don le) ciia HTDH khu vgc.
Thfing kc sfl lifu mua mit dit va phan loai cac HTTT gay mua Idn, kit hgp ding then vdi phin tieh tuang tic mua Idn - dac difm HTDH cic khu vgc cho thiy tai cac khu vgc KV2, KV3 va KV4, d^ic difm HTDH co thuan lgi hon cho hinh thanh mua Idn lien quan din KKL (hudng son van, die diem hinh thai cac day mii chinh, sg hifn difn cua cac diy mil chay ra sat biin, hudng dudng bd bien,,..). CJ eac khu vgc phia nam viing nghien ciiu, mua Idn do KKL don thuin va do KKL ket hgp vdi cic HTTT khac di chiim mgt ty trgng rat cao: 45,9%i d KV2;
64,9% d KV3 va tdi 70,6% d KV4.
Nghifn eim, phan tieh ding thdi mua Ion vi dja hinh nhu tren di phac hga mft cich eg the han die
diem chf dfl mua viing ven bifn Trung Bfl. Su gia ting tan suit cic dgt mua Idn ben quan den yfu tfi KKL fren long so dgt d cic khu vuc phia nam ehi ro trong nguyfn nhan mua Idn d day cd vai tro quan trgng cua sg tuong t i e giua dia hinh vdi nhan to KKL (bao gflm KKL dan thuin, to hgp KKL vdi cac HTTT khac (sfi 4, sfi 6).
Kit q u i nghien cuu nay mgt jnat rat thiit thuc cho cfing tac du bao mua, mua Idn d cac khu vuc dai ven bien Trung Bo, mat khac ciing cho thay each tiep can nghien cuu thien tai mua Idn cua dia ly khi bau la hgp ly va dac biet. Cong trinh dugc hoan thanh trong khuon khfl 2 de tai cap Vien Han lam KHCN Viet Nam [7, 8], hudng "Phong tranh giam nhe thien tai", thuc hien trong cac nam 2008-2009 va 2012-2013.
TAILIEUDAN
[1] Nguyin Dire Ngir, Nguyin Trgng Hieu, 1985: Phan viing Khi hau Viet Nam, Tong cue KTTV. Ha Nfl
[2] Le Vdn Thdo, 2000: Mua Idn d cac tinh mien Trung do tac dgng khong khi lanh vdi nhilu dgng song dong trong ddi gio dfing can nhiet ddi.
Tuyfn tap bao cao hoi nghi "Khoa hoc, cong nghe du bao phuc vu du bao khi tugng thiiy van". Ha Ngi 26 - 27/12/2000, Tflng cue KTTV,
[3] Nguyen Khanh Vdn, 2002: Tinh da dang va phirc tap trong ca che miia mua d dai ven bien Viet Nam. Tap chi Cac Khoa hpc v i Trai Dat, T.24, 3, TT KHTN&CNQG, 209-215.
[4] Nguyen Khanh Vdn, Biii Minh Tang, 2003.
Dac diem cac hinh the thdi tiet gay mua, Iu, lut Idn va dac bift Idn d cac tinh Quang Binh, Quang T n , Thira Thien - Hue. Tap chi Cac Khoa hgc ve Trai Dat sfi dac bift ky nifm 10 nam thanh lip Vifn Dia Iy, Vifn KH&CN Vift Nam, T.25, 4, 339-345,
[5] Nguyin Khanh Vdn. Biii Minh Tdng, 2004:
Dac diem hinh the thdi tiet gay mua, lu, lgt Idn va d i e biet Idn d cac tinh Thanh H o i , Nghf An, H i Tinh, thai ky 1997 - 2 0 0 1 . Tap chi Cac Khoa hgc v i T r a i D i t , T . 2 6 , 1,50-59.
[6] Nguyin Khanh Vdn. Dd Le Thiiy, 2009:
Nguyen nhan v i quy Iuat cua thdi tiet mua Idn,
"mua Idn trai miia'' vimg Bac Trung Bg (giai doan 1987-2006). Tap chi Cac Khoa hgc v i Trai Dit, T.3I, 3, 279-286.
[7] Nguyin Khanh Vdn (chu bien), 2008-2009.
Nghien eiiu nguyen nhan va quy luat boat dgng cua thdi tiet mua Idn sinh lii lut, "mua Idn trai miia" - canh bao va df xuat cac giai phap phong tranh giim nhe thi6n tai d Bac Trung Bg Vift Nam. Bio cao tong kft df tai cap Vifn Khoa hgc va Cong nghf Viet Nam.
[8] Nguyen Khanh Van (chu bien), 2012-2013:
Nghien cuu nguyen nhan, quy Iuat xuat hien cua thdi tiet mua Idn gay lu lut, lut hen quan vdi dia hmh vung Nam Tnmg Bfl Viet Nam; canh bao va de xuat cac giai phap phong tranh giam nhe thifn lai". Ket qua df tai cap Vien Han Iam Khoa hgc va Cong nghe Viet Nam. M i s6: VAST05,0I/12-13.
[9] Nguyin Khanh Vdn, 2012: Vai tro cua hinh thai dja hinh dfli vdi mua Idn d vimg Bac Trung Bf va sg phan hoa giua bac va nam deo Ngang. Tap chi Cac Khoa hgc v i Trai Dat, T.34, 1,10-17.
[10] Yeu Trdm Sinh, 1960: Nguyen ly Khi hau hgc (tap 2), ban dich tir tiing Trung ciia Vu Van Mmh, Pham Quang Trudng. Nxb. Nha Khi tugng, Ha Nf i.
[ I I ] PoMedM: K., 1976: MeTeopojiorHH MyccoHOB. riepeBoa c aurjiHiicKoro na pyccKHii H3tIK. rHflpOMeTeOH3flaT, J l e H H H F p a U .
SUMMARY
The heavy rain differences based on topo-geographlca! analyse at Coastal Central Region, from Thanh Hoa to Khanh Hoa
Following thie article "The Role of lopo-geographical conditions of Northern Central Region Vietnam and the difference of heavy rams between North and South Ngang Pass" [Journal of Sciences of the Earth 1,34, N°1/2012l, this paper present the reseach results of the resonant influences of topo-geographic conditions in heavy rains patterns in Coastal Central Region of Vietnam, those divided into some areas along N-S direction by E-W orientation mountain ranges (Ngang, Hai Van, Ca passes).
Base on the weather situation maps, daily rainfall data (1987-2006) over Coastal Central tenitory (from Thanh Hoa to Khanh Hoa). the count and frequencies of heavy rains occurrence (during this timeline) corresponding lo 7 types of
Synoptic Weather Situation (SWS) - major factor leading to heavy rain - have been analised and evaluated. The results of analysing simultaneously topo-geographic conditions of 4 areas: Northern Ngang Pass (KVl), Ngang Pass to Hai Van Pass (KV2), Hai Van Pass to Ca Pass (KV3) and Southern Ca Pass (KV4) together with SWS show that:
- For the heavy rain caused purely by cold air mass (CAM): in KV1: there are only 7 waves equivalent 10,4% of total number of SWS, while In KV2 there are 41 waves - accupeid 36,9%, in KV3:11 weves ~ 19,3%. and in KV4 there are 13 waves - 38.2%.
- For the heavy rain caused by CAM and combination of CAM with other SWS: in KVl there are 8 waves (11,9% of total numt}er of SWS). in KV2: 51 waves (accounts for 45.9%). in KV3: 37 weves (64,9%) and in KV4 there are 24 weves (70,6%). It meens the sounthem areas have higher havy rain frequence.
The differences in topo-geographic condition of 4 areas, especially the directions of mountain ranges, characteristics of major mountain ranges, the directions of coast line and the presence of some mountain passes (Ngang, Hai Van, Ca], are the main reason leading to the increasing convergence and as the consequently the noticeable increase of heavy rains frequence those relative to CAM.
- The study on the heavy rain differences based on topo-geographical analyse will be a source of valuable information, contributing to more precisely forecast of heavy rams in different areas of Coastal Central Region of Vietnam.
The above approach of geographic climatology to examine the lopo-geographical conditions and heavy rains is a new and reasoable approach, it allows to solve the natural disaster problem more effective and more useful at difference areas in Coastal Central Region of Vietnam.
Tlie study was supported by 2 projects of Vietnam Academy of Sdence and Technology [7, 81, Science brench
"Preventing Disaster Reduction", performed in the years 2008-2009 and 2012-2013.
