Evaluasi kekeringan sawah tadah hujan di dataran rendah Kabupaten Lombok Tengah bagian tengah

HARYAWIDARTO, Asmono, Drs. Suyono, MS

2003 | Tesis | S2 Geografi

Dataran rendah Lombok Tengah bagian tengah terletak dia ntara lereng kaki Gunungapi Rinjani dan Gunung Bonge. Luas sawah sekitar 37.600 ha, pengairan 12 % irigasi teknis, lainnya setengah teknis dan tadah hujan. Keadaan iklim tergolong agak kering. Kekeringan terjadi berulang hingga gaga1 panen padi mencapai has 6 158 ha. Kekeringan berulang belum diketahui secara pasti faktornya. Penelitian bertujuan mengetahui faktor yang berpengaruh terhadap kekeringan : 1) tingkat kekeringan dan agihannya, 2) sebaran kekeringan faktor kondisi fisik lingkungan, 3) intensitas kekeringan faktor variasi oksilasi . Metoda penelitian melalui observasi lapangan dan laboratorium, lokasi sampel dipilih titik stasiun hujan, pengukuran kekeringan faktor lokal dengan mengharkatkan fisik lingkungan, kekeringan faktor global melalui parameter indeks oksilasi. Indeks kekeringan dikalkulasi dari defisit air lengas tanah metode Thornthwaite-Mather menggunakan teknik imbangan neraca air. Data sekunder terdiri variabel iklim, hidrolog, tanaman, lokasi dan data primer variabel tanah hasil laboraturium. Analisis spasial lokasi sebaran kekeringan terhadap indeks wilayah diuji statistik menggunakan Chi Kwadrat, analisis tempral intensitas kekeringan terhadap variasi oksilasi menggunakan korelasi dan regresi. Hasil penelitian menunjukkan bahva imbangan hidrologis neraca air daerah penelitian adalah defisit PE P, indeks kekeringannya tinggi = 35,4 % agihan kekeringan sedang (Ia= 16,7%- i 33,3 YO) seluas 7.680 ha dan kekeringan tinggi ( Ia > 33,3% ) seluas 66.000ha. Faktor-faktor' yang mempengaruhi kekeringan wilayah : 1) variasi SO1 dan anomali iklim sifatnya berubah-ubah, 2) indeks wilayah merupakan tingkat kerentanan fisik lingkungan terhadap kekeringan bersifat tetap, 3) faktor bukan fisik lingkungan karena penympangan proses pola penanaman padi. Evaluasi hubungan korelasi kekeringan dengan indeks oksilasi r = - 0,47 , dengan indeks wilayah r = 0,79 pengujian sebaran (Ia) menurut indeks dayah tidak tejadi perbedaan proporsi kekeringan wilayah saat normal ataupun saat anomali.

The lowland of the central part of Central Lombok lies between Rinjani volcano and Bonge mountain. It has 37.600 ha rice field which is irrigated 12 % technical irrigation, and the rest semi techcal irrigation and rainfed irrigation. The climate is dry and recurrent drought makes failed in harvest up to 6,158 ha. The factors affecting the drought are yet identifiable. The research aims at identifLing the factors for the drought, especially to find out: 1) the degree and dstribution of the drought, 2) the distribution of drought of the physical environment factors, 3) the intensity of drought of the oscillation variation factors. The research is conducted in the field and laboratory. The location of the research is chosen among the sites of rain observation station. The measurement of local drought is based on the physical environment, while the global drought is on the relation of oscillation index parameter. The aridity index is calculated from the water deficit of soil moisture using Thornthwaite-Mather by applying water-balance technique. The secondary data consist of variables of climatic elements, hydrology, plants, and locations. Meanwhile, the primary data are the variables of soil derived from the laboratory test result. The spatial analysis of drought distribution on the regional index is tested stastitically using ehl Square and the temporal analysis of dryness intensity on the oscillation variation is done on the correlation and regression method. The findings show that the hidrologic equity of water balance in the research area is deficit with EP>P, the aridity index is high = 35,44%, the distribution of medium drought ( Ia=l6,7-<33,3%) coverq' 7.680 ha and high drought ( Ia133,3%) covers 66.000 ha. The factors affecting the, regional dryness are : 1) The changes of SO1 variation and the climate anomaly, 2) the regional index that indicates constant vulnerability level of the physical environment to drought, 3) non physical factor owing to space-time deviation in the rice planting process. The evaluation on the correlation between the drought and oscillation is(r =- 47, the dryness and the regional index is r = 0,79 The evaluation on the correlation between the the dryness and oscillation is distribution (la) according to the regonal index shows no different between the proportion of regional dryness during the normal climate and during the anomaly

Kata Kunci : Sawah Tadah Hujan,Dataran Rendah,Evaluasi Kekeringan