Abstract
This study investigates the variation of seasonal streamflow and streamflow extremes in five catchments of the Mahaweli River Basin (MRB) Sri Lanka from 1990 to 2014, and the relationship between streamflow and seasonal rainfall in each catchment is then examined. Furthermore, the influence of Indian Ocean Dipole (IOD) and El Nino and Southern Oscillation (ENSO) on the seasonal rainfall and streamflow in the upper (UMRB) and lower reaches (LMRB) of MRB are explored. It’s found that the rainfall amount in southwest monsoon (SWM) season contributes 29.7% out of annual total rainfall in the UMRB, while the LMRB records 41% of the total rainfall during the northeast monsoon (NEM) season. The maximum streamflow of upper (lower) Mahaweli catchments is observed in the SWM (NEM) season. Catchments in the UMRB (LMRB) recorded strong interannual variability of seasonal overall flow (Q50), Maximum 10-day, and 30-day flows during the SWM (NEM) season. It’s further revealed that the catchment streamflow in the UMRB is closely correlated with the SWM rainfall in the interannual time scale, while streamflow of catchments in the LMRB is closely associated with the NEM rainfall. The effects of ENSO and IOD on streamflow are consistent with their impacts on rainfall for all catchments in MRB, with strong seasonal dependent. These suggested that the sea surface temperature anomalies in the both Indian Ocean and tropical Pacific Ocean are important factors affecting the streamflow variability in the MRB, especially during the SWM season.
Highlights
The hydrologic cycle at the watershed scale reflects the complex interactions among climate, land use, and land cover changes (LULC), soil properties, geology, and terrain [1]
It’s further revealed that the catchment streamflow in the upper Mahaweli river basin (UMRB) is closely correlated with the southwest monsoon (SWM) rainfall in the interannual time scale, while streamflow of catchments in the lower Mahaweli river basin (LMRB) is closely associated with the northeast monsoon (NEM) rainfall
These suggested that the sea surface temperature anomalies in the both Indian Ocean and tropical Pacific Ocean are important factors affecting the streamflow variability in the Mahaweli River Basin (MRB), especially during the SWM season
Summary
The hydrologic cycle at the watershed scale reflects the complex interactions among climate, land use, and land cover changes (LULC), soil properties, geology, and terrain [1]. Streamflow is the most important component of the hydrological cycle, which directly links to water resources management. Alterations in the long-term discharge of streamflow can be caused by decadal or inter-decadal climate variability, and anthropogenic activates such as LULC in the upstream basin, construction of reservoirs [4], and diversion of water for irrigation [5,6]. Precipitation variability [7] and LULC [8] in the watershed are the two most likely drivers of long-term discharge modifications in a large river basin. Pascolini-Campbell et al [9] found that natural precipitation variability influenced by interannual to decadal ENSO variability is the main cause for observed inter-annual variability of Gila River flow. Panda et al [10] revealed that intensified interannual variability of the Mahanadi streamflow is occurred due to the moving variability of
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