Modelling the crop water and irrigation requirements using CROPWAT model: a case study in arid and semi-arid regions of Pakistan

Water is a key factor in global food security, which is critical to agriculture. Dwindling water resources and increasing food demands require greater efficiency in water use, particularly in arid and semi-arid regions. Regulated deficit irrigation provides a means of reducing water consumption while minimizing adverse effects on yield. Models can play a useful role in developing practical recommendations for optimizing crop production under water-scarce conditions. Therefore, the current study was conducted to estimate crop water requirements (CWRs), net irrigation requirements (NIRs), and effective rainfall (Peff) for wheat crop in arid (Bahawalpur) and semi-arid regions (Faisalabad) of Pakistan. Precipitation and temperature data predictions are derived from four pre-validated Coupled Model of the Intercomparison Project Phase 5 (CMIP5) of Global Climate Models (GCMs), namely i) MIROC5, ii) IPSL-CM5A_MR, iii) NorESM1-M and iv) CCSM4. Model data, including the geo-coordinates of the area, temperatures, relative humidity, solar radiation/sunshine hours, crop evapotranspiration and soil data, have been used as input to CROPWAT for simulation of CWR, NIR and Peff in a historical period (1986-2005) and four consecutive future time series (2020-2039, 2040-2059, 2060-2079 and 2080-2099). The results showed that during the wheat growing season, CWR and NIR continued to increase. By the end of the 21st century, the CWR in semi-arid and arid areas of representative concentrated pathways (RCPs 4.5 and 8.5) increased by 3.01-6.86% and 2.46-5.64%, respectively. By 2099, under RCPs 4.5 and 8.5, the NIR in semi-arid and arid areas will increase by 5.49-10% and 2.41-5.86%, respectively. In the semi-arid and arid areas, the average seasonal Peff will be reduced by 9.79% (RCP 4.5), 10.07% (RCP 8.5), 2.81% (RCP 4.5), and 3.16% (RCP 8.5), respectively. Therefore, semi-arid areas will be more affected than arid areas, and changes in climatic conditions will threaten the agricultural system by reducing Peff.