Abstract The Indus Basin Irrigation System (IBIS) of Pakistan is a major user of surface and groundwater and provides food and economic security for about 207 million people. To assess the impact of agricultural development on water resources, we developed surface water balances for its canal commands and examined trends from 1981‐82 to 2012‐13. In this semi-arid environment, crop water use is the major water balance term. We estimated it by computing actual evapotranspiration (ETa) from two different remote sensing methods, ETLook and CMRSET, to account for method uncertainty. Net groundwater use was a small component of the water balance in most canal commands, particularly in the Sindh province. The measured or estimated known terms in the water balance did not result in its closure; and a balance term of unaccounted outflows and inflows was required to close it. Measured and readily estimated components amounted to 80 – 90% of the water balance components, with unaccounted inflows and outflows accounting for the remaining 10 – 20%. Of the measured water balance terms, rainfall showed no statistically significant trend in any canal command, whereas canal deliveries decreased significantly in many canal commands. Overall, ETa generally increased in Punjab and decreased slightly in Sindh. The magnitude of the increases in ETa differed between the ETLook and CMRSET estimates. The historical trends in the balance term (unaccounted outflows and inflows) together with falling groundwater levels show that water use is becoming less sustainable in several canal commands, especially in the Punjab province. The trend to a less sustainable position results particularly from water use in the dry Rabi season.

中文翻译：

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灌溉渠命令的水平衡趋势及其对巴基斯坦可持续水资源管理的影响：1981 年至 2012 年的证据

摘要 巴基斯坦的印度河流域灌溉系统 (IBIS) 是地表水和地下水的主要用户，为约 2.07 亿人提供粮食和经济安全。为了评估农业发展对水资源的影响，我们为其运河命令制定了地表水平衡，并检查了 1981-82 至 2012-13 年的趋势。在这种半干旱环境中，作物用水是主要的水平衡术语。我们通过计算来自两种不同遥感方法 ETLook 和 CMRSET 的实际蒸散量 (ETa) 来估计它，以解释方法的不确定性。在大多数运河指挥区，尤其是在信德省，地下水净使用量只是水平衡的一小部分。水平衡中测量或估计的已知项并未导致其关闭；并且需要一个未计入的流出和流入的平衡期限来关闭它。测量和易于估计的部分占水平衡部分的 80-90%，未计入和流出占其余 10-20%。在测量的水平衡项中，降雨量在任何运河命令中都没有显示出统计上的显着趋势，而在许多运河命令中，运河输送量显着下降。总体而言，ETa 在旁遮普省普遍增加，在信德省略有下降。ETLook 和 CMRSET 估计之间的 ETa 增加幅度不同。平衡项的历史趋势（未计入的流出和流入）以及地下水位下降表明，在几个运河指挥区，特别是在旁遮普省，用水的可持续性正在下降。