Precipitation Trends over the Indus Basin

Abstract

A large population relies on water input to the Indus basin, yet basinwide precipitation amounts and trends are not well quantified. Gridded precipitation data sets covering different time periods and based on either station observations, satellite remote sensing, or reanalysis were compared with available station observations and analyzed for basinwide precipitation trends. Compared to observations, some data sets tended to greatly underestimate precipitation, while others overestimate it. Additionally, the discrepancies between data set and station precipitation showed significant time trends in such cases, suggesting that the precipitation trends of those data sets were not consistent with station data. Among the data sets considered, the station-based Global Precipitation Climatology Centre (GPCC) gridded data set showed good agreement with observations in terms of mean amount, trend, and spatial and temporal pattern. GPCC had average precipitation of about 500 mm per year over the basin and an increase in mean precipitation of about 15% between 1891 and 2016. For the more recent past, since 1958 or 1979, no significant precipitation trend was seen. Among the remote sensing based data sets, the Tropical Rainfall Measuring Mission Multi-Satellite Precipitation Analysis (TMPA) compared best to station observations and, though available for a shorter time period than station-based data sets such as GPCC, may be especially valuable for parts of the basin without station data. The reanalyses tended to have substantial biases in precipitation mean amount or trend relative to the station data. This assessment of precipitation data set quality and precipitation trends over the Indus basin may be helpful for water planning and management.

Spatio-Temporal Variability of Drought in Pakistan Using Standardized Precipitation Evapotranspiration Index

“…Drought characteristics averaged for every 15 years revealed worrisome outcomes for zones 4 and 5. The drought count was at a maximum for the period 2000-2015 in zones 4 (27) and 5 (24). Similarly, the mean drought duration was maximum in zone 4 at 3.815 months.…”

“…In addition, the SPEI drought index used here was based on one specific dataset (CRU) of precipitation and other climate fields. A recent evaluation of numerous precipitation products in the Indus Basin, which includes most of Pakistan, found that the CRU precipitation field appears to have realistic mean amount and long-term trends relative to station observations, suggesting that temporal homogeneity and bias are on the whole successfully controlled by CRU's interpolation and quality control procedures [27]. However, a sensitivity analysis, possibly including intercomparison to SPEI derived from other historic climate datasets, would help confirm the drought patterns and trends seen here.…”

“…Trend analyses were then performed on each of the zones' SPEI and on drought characteristics using the Modified Mann-Kendall test. Total annual precipitation varies from less than 250 mm in the south to 2000 mm in the north [25,27]. Two main precipitation systems produce rains in Pakistan.…”

“…Due to the number of stations contributing to the dataset varying throughout time, the dataset is not necessarily homogeneous; however, previous studies on trend analysis using CRU dataset have shown promising results [32]. A recent study on the Indus Basin by Krakauer et al [27] concluded that, despite poor representation of the spatial distribution of precipitation over the Indus Basin using the CRU dataset, the temporal trend of precipitation compared well with that calculated using more stations.…”

Drought Trends in Balochistan

“…The northeastern parts of the province are within the Indus Basin. A recent study examined the precipitation trends over the entire Indus Basin [25]. Monsoon winds bring summer rainfall, whereas westerly disturbances cause winter precipitation in the province.…”