Relating Urbanization and Irrigation Water Demand in Gujranwala District of Pakistan

The estimation of crop water requirement (CWR) is an important aspect in efficient usage of water, especially in regions where water is scarce. This study estimates the change in agricultural land of major crops in Gujranwala District due to urbanization using remote sensing. The irrigation water demand (IWD) and irrigation cost are computed for the study years of 1992, 1995, 2000, 2008, 2014, and 2016. Wheat and rice are studied as they are the major crops grown in the district. Remote sensing image classification was used to prepare the land use maps and estimate cropping area. Evapotranspiration-based CWR was estimated using ETo calculator from FAO and crop coefficient (K-c) of each crop. Finally, using the water pricing for the province, change in cost of irrigation due to variation in IWD is computed. The results show that the urban area has doubled from 20 to 40 thousand hectares between 1992 and 2016 with the area sown under wheat and rice decreased by 10% and 19%, respectively. The CWR value for 2016 was 381 and 605 mm/season for wheat and rice, respectively. Between 1992 and 2016, IWD of wheat [measured in million acre-feet/year (MAF)] decreased from 0.83 to 0.70 whereas it reduced from 1.47 to 1.03 MAF for rice. During this period, the total cost of water (in million USD) for wheat varied between 0.65 and 0.33 and for rice varied between 1.69 and 0.84. Use of remotely sensed image displayed the spatiotemporal distribution of urban expansion as well as of wheat and rice within the district. This information can play a key role in tracking the state of agricultural activity and efficient agricultural water distribution.