Assessment of the impact of climate change and mining activities on streamflow and selected metal's loading in the Chindwin River, Myanmar.

The rapid expansion in mining activities is deteriorating the water quality in the Chindwin River of Myanmar. In addition, climate change may also aggravate this situation in future. Therefore, the aim of this study was to establish a connection between hydrology, mining area, heavy metal loading, and climate change in the Chindwin River. The hydrology of the upper Chindwin basin was modelled using SHETRAN hydrological model. Geochemical model PHREEQC was utilised to conduct speciation and saturation indexes modelling along the river in order to quantify the precipitated minerals along the river. Thereafter a regression relationship along with LOADEST model was used to quantify the heavy metal loads. Future climate was projected using four RCM's namely ACCESS1-CSIRO-CCAM, CCSM4-CSIRO-CCAM, CNRM-CM5-CSIRO-CCAM and MPI-ESM-LR-CSIRO-CCAM. Future discharges at water quality monitoring stations were simulated using the averaged ensembles. Finally, the heavy metal loading under future climate scenarios were analysed. Results indicate that climate change is likely to reduce future discharges by 3.4%-36.5% in all stations except in the Mokekalae station which shows 1.3%-9.4% increase in the near future discharges. Also, the projected metal loading under future climate conditions shows a decreasing pattern which is similar to the projected discharge pattern. In both baseline and future climate conditions, the area between stations Naung Po Aung and Uru downstream show the highest load effluent for both arsenic and mercury while the area between stations Uru downstream and Mokekalae show the highest load of iron effluent. Although future heavy metal loadings are expected to decrease, mining activities should be carefully monitored, since they discharge a large amount of toxic heavy metal loadings into the Chindwin River which is also expected to suffer a decrease streamflow in future.

Shrestha S ，Gunawardana SK ，Piman T ，Babel MS ... -  《-》

Assessment of climate change impacts on water balance and hydrological extremes in Bang Pakong-Prachin Buri river basin, Thailand.

Among many factors the hydrology of a watershed is mainly influenced by climate and land use change. This study examined the impacts of climate change on water resources and extreme events in the Bang Pakong-Prachin Buri River Basin, Thailand using three different Regional Climate Models (RCMs) ACCESS1-CSIRO-CCAM, CNRM-CM5-CSIRO-CCAM, and MPI-ESM-LR-CSIRO-CCAM under RCP4.5 and RCP8.5 emission scenarios. Soil and Water Assessment Tool (SWAT) was used to simulate the future streamflow and Extreme Value Type I distribution (EVI) was used to analyze the extreme events under projected climate conditions. The result of this study showed an increase in maximum (1.9 °C/3.6 °C) and minimum (1.6 °C/3.3 °C) temperatures under RCP4.5/8.5 at the end of the 21st century. In addition, projected rainfall is expected to decrease up to 6.8% (8.5%) in 2050s and then increase slowly such that the decrement remains 4.2% (11.0%) under RCP4.5 (RCP8.5) at the end of the century. The rainfall pattern is projected to considerably fluctuate, in particular, a shift in long term average annual peak event from September to August is predicted in 2080s under emission scenario RCP4.5 (RCP8.5). On the other hand, the average annual discharge is expected to increase up to 13.5% (2020s) and 7.6% (2050s) under RCP4.5 and RCP8.5 respectively with decreasing trend in low flows and increasing trend in high flows. Further analysis on extreme events; strengthened the results from hydrological modeling with an increase in flow volume for the same return period under changed climate conditions. This raises water resources management issues in the Bang Pakong-Prachin Buri River Basin regarding the frequency of flood and drought events in the future calling for proper policy formulation and implementation.

Okwala T ，Shrestha S ，Ghimire S ，Mohanasundaram S ，Datta A ... -  《-》

Mapping groundwater resiliency under climate change scenarios: A case study of Kathmandu Valley, Nepal.

Groundwater resources of Kathmandu Valley in Nepal are under immense pressure from multiple stresses, including climate change. Due to over-extraction, groundwater resources are depleting, leading to social, environmental and economic problems. Climate change might add additional pressure by altering groundwater recharge rates and availability of groundwater. Mapping groundwater resilience to climate change can aid in understanding the dynamics of groundwater systems, facilitating the development of strategies for sustainable groundwater management. Therefore, this study aims to analyse the impact of climate change on groundwater resources and mapping the groundwater resiliency of Kathmandu Valley under different climate change scenarios. The future climate projected using the climate data of RCM's namely ACCESS-CSIRO-CCAM, CNRM-CM5-CSIRO-CCAM and MPI-ESM-LR-CSIRO-CCAM for three future periods: near future (2010-2039), mid future (2040-2069) and far future (2070-2099) under RCP 4.5 and RCP 8.5 scenarios were bias corrected and fed into the Soil and Water Assessment Tool (SWAT), a hydrological model, to estimate future groundwater recharge. The results showed a decrease in groundwater recharge in future ranging from 3.3 to 50.7 mm/yr under RCP 4.5 and 19-102.1 mm/yr under RCP 8.5 scenario. The GMS-MODFLOW model was employed to estimate the future groundwater level of Kathmandu Valley. The model revealed that the groundwater level is expected to decrease in future. Based on the results, a groundwater resiliency map of Kathmandu Valley was developed. The results suggest that groundwater in the northern and southern area of the valley are highly resilient to climate change compared to the central area. The results will be very useful in the formulation and implementation of adaptation strategies to offset the negative impacts of climate change on the groundwater resources of Kathmandu Valley.

Shrestha S ，Neupane S ，Mohanasundaram S ，Pandey VP ... -  《-》

Evaluating the impacts of climate and land-use change on the hydrology and nutrient yield in a transboundary river basin: A case study in the 3S River Basin (Sekong, Sesan, and Srepok).

Assessment of the climate and land-use change impacts on the hydrology and water quality of a river basin is important for the development and management of water resources in the future. The objective of this study was to examine the impact of climate and land-use change on the hydrological regime and nutrient yield from the 3S River Basin (Sekong, Srepok, and Sesan) into the 3S River system in Southeast Asia. The 3S Rivers are important tributaries of the Lower Mekong River, accounting for 16% of its annual flow. This transboundary basin supports the livelihoods of nearly 3.5 million people in the countries of Laos, Vietnam, and Cambodia. To reach a better understanding of the process and fate of pollution (nutrient yield) as well as the hydrological regime, the Soil and Water Assessment Tool (SWAT) was used to simulate water quality and discharge in the 3S River Basin. Future scenarios were developed for three future periods: 2030s (2015-2039), 2060s (2045-2069), and 2090s (2075-2099), using an ensemble of five GCMs (General Circulation Model) simulations: (HadGEM2-AO, CanESM2, IPSL-CM5A-LR, CNRM-CM5, and MPI-ESM-MR), driven by the climate projection for RCPs (Representative Concentration Pathways): RCP4.5 (medium emission) and RCP8.5 (high emission) scenarios, and two land-use change scenarios. The results indicated that the climate in the study area would generally become warmer and wetter under both emission scenarios. Discharge and nutrient yield is predicted to increase in the wet season and decrease in the dry. Overall, the annual discharge and nutrient yield is projected to increase throughout the twenty-first century, suggesting sensitivity in the 3S River Basin to climate and land-use change. The results of this study can assist water resources managers and planners in developing water management strategies for uncertain climate change scenarios in the 3S River Basin.

Trang NTT ，Shrestha S ，Shrestha M ，Datta A ，Kawasaki A ... -  《-》

Hydrological modelling of a snow/glacier-fed western Himalayan basin to simulate the current and future streamflows under changing climate scenarios.

Himalayan rivers are the paramount source of water supply to millions of people in northern India for drinking, irrigation and hydropower generation. Several researches reported that the hydrological regime of these Himalayan rivers is vulnerable to climate change. In order to understand the hydrologic response of their headwaters and examine the climate change impacts on streamflow, a hydrological modelling study is carried out in the upper part of the Satluj river basin in western Himalaya by using a temperature index based SWAT (Soil Water Assessment Tool) model. The model performed well for both calibration (years 1986-2000) and validation (2001-2005) periods against the observed daily streamflow at Rampur (R2 ≈ 0.9 and NSE ≥ 0.85). The study reveals that having a larger snow covered area, the snowmelt runoff is the major contributor to the Satluj river discharge at Rampur that comes out to be about 68-71% of the average annual water yield of about 600 mm. The actual evapotranspiration comes out to be about 14% of precipitation. The water yield of the basin is about 50% of the precipitation, for which the major part is generated in early summer. Further, to study the climate change impact on future streamflow, the downscaled data of CORDEX CCSM4 under two Representative Concentration Pathways (RCP4.5 and RCP8.5) scenarios are used. The bias correction is applied at point level to remove biases from future time series of downscaled data and subsequently loaded into the SWAT model to simulate the future streamflows at the end of the century. The future climate variability in terms of precipitation and temperature exhibited that the climate in the region would become wetter and warmer. A 14% to 21% of increase in annual precipitation is predicted towards the end of the century from the current average annual precipitation of about 420 mm under RCP4.5 and RCP8.5, respectively. Similar to precipitation, the temperature will also be increased by 2.18 °C to 5.71 °C (in both the RCPs) than the current temperature values. The changed climate conditions in future are transformed into the possible range of stream flows using the SWAT model and found that the future climate would increase the streamflow by over 11%-19% at the end of the century under RCP4.5 and RCP8.5 scenarios, respectively. The outcome of this study can be used to develop the suitable strategies for sustainable water management in the region.

Shukla S ，Jain SK ，Kansal ML 《-》