Comprehensive Water Requirement Of Kaibu Subregion Of Pengbo Irrigation District In Tibet Lhasa

Tibet is one of the biggest area for the increasing of crop production and income in China. Kaibu subregion of Pengbo irrigation district is located in a valley with a very good condition of agricultural development in in Tibet Lhasa. With the acceleration of agriculture modernization, the assessment of the multi-aspects water demand and reasonable disposition of water resources in the irrigation district, are of great significance to agricultural development and increasing grain yield. This study systematically investigated the proportion of the main crops planting, physical geographical condition and population state in Kaibu subregion, in order to assess the agricultural water demand, domestic water demand and ecological water demand, as well as the comprehensive water requirement under different reliability. Considering the available water supply in Kaibu subregion, water supply and demand balance in this area was analyze. The main research conclusions are as follows:1. According to the FAO Penman-Monteith method, Reference crop evapotranspiration(ETo) in Kaibu subregion was calculated. ETo under different reliability were respectively 1056.95 mm for P=25%, 1103.19 mm for P=50% and 1137.13 mm for P=25%.2. The evapotranspiration(ET) of highland barley in Kaibu subregion under different reliability was respectively 362.1 mm for P=25%, 396.7 mm for P=50% and 434.6 mm for P=25%; the ET of winter wheat there was respectively 626.5 mm for P=25%, 667.4 mm for P=50% and 705.1 mm for P=25%; the ET of oilseed rape was respectively 386.2 mm for P=25%, 423.5 mm for P=50% and 454.1 mm for P=25%; the ET of potato was respectively 309.4 mm for P=25%, 337.8 mm for P=50% and 369.3 mm for P=25%.3. Kaibu river supports the water supply of Kaibu irrigation district. The total water flows under different reliability were respectively 4971.8×104m3 for P=50% and 4002.7×104m3. The water flow is much larger from June to October than other months.4. Based on the proportion of the main crops planting and population state in the year of 2011, the total water demand under reliability of P=50% was 1542.5×104m3, and the percentage rates for different water demand were respectively agricultural water demand 3.84%, domestic water demand 0.07% and ecological water demand 27.12%; the total water demand under reliability of P=75% was 1293.4×104m3, and the percentage rates for different water demand were respectively agricultural water demand 5.54%, domestic water demand 0.08% and ecological water demand 26.69%. In the future year of 2020 after the adjustment of agricultural planting structure, the total water demand under reliability of P=50% was 1722.7×104m3, and the percentage rates for different water demand were respectively agricultural water demand 7.42%, domestic water demand 0.11% and ecological water demand 27.12%; the total water demand under reliability of P=75% was 1502.7×104m3, and the percentage rates for different water demand were respectively agricultural water demand 10.72%, domestic water demand 0.14% and ecological water demand 26.69%.The analysis of water resources supply and demand balance indicate that the water supply in Kaibu subregion can satisfy the comprehensive water requirement for now, but in May this district would come through a water shortage phenomenon by 2020 which will reach 10-22×104m3. Nowadays, Kaibu subregion is in the face of remaining water resources uneven distribution problem and a relative low water use efficiency, which should be paid enough attention.