Catchment scale assessment of drought impact on environmental flow in the Indus Basin, Pakistan
Abstract. The impact of drought on environmental flow (EF) in 27 catchments of the Indus basin is studied from 1980–2018 using the Indicators of Hydrologic Alterations (IHA). The standardized Precipitation Evapotranspiration Index (SPEI) was systematically propagated from one catchment to another using principal component analysis (PCA). Threshold regression is used to determine the severity of drought (scenario-1) and month (scenario-2) that trigger low flows in the Indus Basin. The impact of drought on low EFs is quantified using the Range of variability analysis (RVA). The hydrological alteration factor (HAF) is calculated for each catchment in the Indus basin. The results show that most of the catchments are vulnerable to drought during the periods 1984–1986, 1991/1992, 1997 to 2003, 2007 to 2008, 2012 to 2013, and 2017 to 2018. On a higher time scale (SPEI-12), drought is more severe in Lower Indus Basin (LIB) than in the Upper Indus Basin (UIB). IHA pointed out that drought significantly impacts the distribution of environmental flow components, particularly extreme low flow (ELF) and low flow (LF). The magnitude and frequency of the ELF and LF events increase as drought severity increases. The threshold regression provided useful insights indicating that moderate drought can trigger ELF and LF at shorter time scales (SPEI-1 and SPEI-6) in the UIB and Middle Indus Basin (MIB). Conversely, severe and extreme drought triggers ELF and LF at higher time scales (SPEI-12) in LIB. The threshold regression also divided the entire study period (1980–2018) into different time zones (scenario-2), which is useful in quantifying the impact of drought on low EFs using the SPEI coefficient. Higher SPEI coefficients are observed in LIB, indicating high alterations in EF due to drought. HAF showed high alterations in EF in most of the catchments throughout the year except in August and September. The alterations are subject to several factors, including climate change, seasonality of the river flow, land use changes, topography, and anthropogenic activities. Overall, this study provided useful insights for analyzing the effects of drought on EF, especially during low flows.
Khalil Ur Rahman et al.
Status: final response (author comments only)
RC1: 'Comment on nhess-2023-4', Anonymous Referee #1, 06 Apr 2023
- AC1: 'Reply on RC1', Songhao Shang, 18 May 2023
RC2: 'Comment on nhess-2023-4', Anonymous Referee #2, 20 Apr 2023
- AC2: 'Reply on RC2', Songhao Shang, 18 May 2023
Khalil Ur Rahman et al.
Khalil Ur Rahman et al.
Viewed (geographical distribution)
This is a comprehensive manuscript which discuss the environmental flows and droughts in the entire Indus basin in Pakistan. Overall manuscript is well written, figures and results are well presented and conclusions are valuable. However, the quality of manuscript needs to be further improved,here are few comments which may be useful in this regards.
1. In abstract section authors concluded " The alterations are subject to several factors, including climate change,
seasonality of the river flow, land use changes, topography, and anthropogenic activities" which type of analysis have been performed to reach these conclusions which seems to be generic.
2. In the Introduction section authors stated "The Indus River basin is one of the typical basins facing substantial climate and land use changes, resulting in limited water availability". However, no references have been added to support this statement authors should state which part of the Indus basin has faced serious land use and climate changes?
3. How did the authors catagorised the flow data into extreme low flow and low flow?
4. Various data qualities issues have been reported regarding the hydrological and meterological datasets of the Indus basin. How authors addressed the missing datasets and which type of analysis have been performed to check the data quality?
5. On which basis authors have done the demarcation of the indus basin into UIB, MIB and LIB?
6. Various studies have been performed to understand the drought in the Indus basin Authors can open the scholar and search from key word droughts in Indus basin. However, no discussion has been performed to compare the results of this study with literature. Discussing the results with previous studies will be useful for readers and this manuscript has potential to be extended for a brief discussion.
7. I have some minor comments regarding use of abbreviations which are unnecessary , should be reduced and must be explained at first use e.g. In abstract section authors should explain EFs before first use.