Performance Assessment of Human Controlled Irrigation System in the Semi-arid Punjab of Pakistan

Introduction: Irrigation system evaluation is key to its optimal utilization, particularly in human driven system like the Rechna Doab in Punjab, Pakistan. Reallocation of water is only possible by its comprehensive performance assessment. Traditional techniques on local scales are not enough for system evaluation, and thus to manage water resources effectively. Their major limitation is to focus only on internal system processes that deal mainly on-farm irrigation management. The external indicators, which relate system outputs to inputs, were missing until the last few years before introduction of remotely sensed data for estimation of spatially distributed evapotranspiration.

Methods: We estimated actual evapotranspiration (ET_a) according to Surface Energy Balance Algorithm (SEBAL), using Moderate Resolution Imaging Spectroradiometer (MODIS) images for 2006-2015. The plausibility analysis of SEBAL results were carried out with advective-aridity based ET_a. Irrigation performance assessment was carried out by incorporating three indicators including overall consumed ratio (ep), relative water supply (RWS), and crop water deficit (CWD) both for kharif (i.e. summer), and rabi (i.e. winter) cropping seasons.

Results: The assessment of ep showed that irrigation water was never sufficient as their values were found always greater than permissible value. Moreover, variability was found higher during kharif with opposite trends between the upper and lower regions. Regarding RWS, water supply was inadequate, as values were found greater than the permissible limit of 2.0 (Molden et al., 1998) with more severity during kharif seasons. Moreover, RWS values were found higher (especially during kharif) in the lower regions, indicating less adequacy. During rabi, the trend was linear, showing no spatial variation. According to CWD, irrigation demand was considerably higher throughout the year as observed always larger than 30 mm.month^-1 (Bastiaanssen et al., 2001). We concluded that less irrigation water was available in the region, and severity was more during kharif. Nevertheless, the upstream regions in the proximity of irrigation source could be advantageous for receiving better irrigation supply. Further concluded that augmented irrigation through groundwater use cannot entirely satisfy crop water requirements.