Integrated Approach for the Assessment and Development of Groundwater Resources in Arid Lands: Applications in the Quetta Valley, Pakistan

Abstract

The lack of adequate field measurements (e.g., precipitation and stream flow) and difficulty in obtaining them often hampers the construction and calibration of rainfallrunoff models over many of the world’s watersheds, leaving key elements of the hydrologic cycle unconstrained. We adopted methodologies that rely heavily on readily available remote sensing datasets as viable alternatives and useful tools for assessing, managing, and modeling the water resources of such remote and inadequately gauged regions. The Soil and Water Assessment Tool was selected for continuous (1998–2005) rainfall-runoff modeling of the northeast part of the Pishin Lora basin (NEPL), a politically unstable area that lacks adequate rain gauge and stream flow data. To account for the paucity of rain gauge and stream flow gauge data, input to the model included satellite-based Tropical Rainfall Measuring Mission TRMM precipitation data. Modeled runoff was calibrated against satellite-based observations including: (1) monthly estimates of the water volumes impounded by the Khushdil Khan (latitude 30° 40'N, longitude 67° 40'E) and the Kara Lora (latitude 30° 34'N, longitude 66° 52'E) reservoirs, and (2) inferred wet versus dry conditions in streams across the NEPL throughout this period. Calibrations were also conducted against observed flow reported from the Burj Aziz Khan station at the NEPL outlet (latitude 30°20'N; longitude 66°35'E). Model simulations indicate that (1) average annual precipitation (1998–2005), surface runoff, and net recharge are 1,300 × 106 m3, 148 × 106 m3, and 361 × 106 m3, respectively; (2) within the NEPL watershed, precipitation and runoff are high for the northeast (precipitation: 194 mm/year; runoff: 38 × 106 m3/year) and northwest (134 mm/year; 26 × 106 m3/y) basins compared to the southern basin (124 mm/year; 8 × 106 m3/year); and (3) construction of delay action dams in the northeast and northwest basins of the NEPL could increase recharge from 361 × 106 m3/year up to 432 × 106 m3/year and achieve sustainable extraction. The adopted methodologies are not a substitute for traditional approaches that require extensive field datasets, but they could provide first-order estimates for rainfall, runoff, and recharge in the arid and semi-arid parts of the world that are inaccessible and/or lack adequate coverage with stream flow and precipitation data.