On an annual basis, the water theoretically available to Bangladesh is huge in relation todemands. The annual rate of reference crop evapotranspiration (ET 0 ) is around 1500 mm/yearand the annual average rainfall is some 2200mm. In addition, a volume of some 1010 Billionm 3 enters the country in the 57 rivers which cross its border with India and Myanmar, whichcorresponds to a further 6800mm over its surface of 147,570 km 2 , for a total of 9000mm, fourtimes ET 0 . Regional balance of rainfall and evapotranspiration as presented in Table 4 showswater abundance in wet season and shortage in dry season.The surface water available for development in the regional rivers in the dry season(November to May) was estimated by the Master Plan Organization (MPO) for the period1989-1990 as shown in Table 5.These figures are small when divided by the net cultivable area (NCA in Mha) in each region,and compared with ET 0 as shown in Table 6. In the South West, the surface water availablein March of 7 mm and the dependable rainfall of 27 mm, together amount to only 22% of ET 0 .However, there is a large groundwater reservoir, which is replenished by monsoon rainfalland flooding, and is tapped by shallow tubewells (STW) in the dry season.
On an annual basis, the water theoretically available to Bangladesh is huge in relation to<br>demands. The annual rate of reference crop evapotranspiration (ET 0 ) is around 1500 mm/year<br>and the annual average rainfall is some 2200mm. In addition, a volume of some 1010 Billion<br>m 3 enters the country in the 57 rivers which cross its border with India and Myanmar, which<br>corresponds to a further 6800mm over its surface of 147,570 km 2 , for a total of 9000mm, four<br>times ET 0 . Regional balance of rainfall and evapotranspiration as presented in Table 4 shows<br>water abundance in wet season and shortage in dry season.<br>The surface water available for development in the regional rivers in the dry season<br><br>如表5所示,总体规划组织(MPO)对1989年至1990年期间(11月至5月)的估算值如表5所示。<br>如果将这些数字除以每个地区的可耕种净面积(Mha中的NCA),<br>并与ET 0如表6所示。在西南地区,<br>3月份可用的地表水为7毫米,可降水量为27毫米,合计仅占ET 0的22%。<br>但是,有一个大型的地下水库,在季风降雨<br>和洪水的补充下,在枯水期被浅管井(STW)挖掘。
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