Water quality modelling of the Mekong River basin: Climate change and socioeconomics drive flow and nutrient flux changes to the Mekong Delta

Abstract

25The Mekong delta is recognised as one of the world's most vulnerable mega-deltas, being 26 subject to a range of environmental pressures including sea level rise, increasing population, 27and changes in flows and nutrients from its upland catchment. With changing climate and 28 socioeconomics there is a need to assess how the Mekong catchment will be affected in 29terms of the delivery of water and nutrients into the delta system. Here we apply the 30Integrated Catchment model (INCA) to the whole Mekong River Basin to simulate flow and 31water quality, including nitrate, ammonia, total phosphorus and soluble reactive phosphorus. 32The impacts of climate change on all these variables have been assessed across 24 river 33 reaches ranging from the Himalayas down to the delta in Vietnam. We used the UK Met 34Office PRECIS regionally coupled climate model to downscale precipitation and temperature 35to the Mekong catchment. This was accomplished using the Global Circulation Model GFDL-36CM to provide the boundary conditions under two carbon control strategies, namely 37representative concentration pathways (RCP) 4.5 and a RCP 8.5 scenario. The RCP 4.5 38 scenario represents the carbon strategy required to meet the Paris Accord, which aims to 39 limit peak global temperatures to below a 2 o C rise while seeking to pursue options that limit 40 temperature rise to 1.5 o C. The RCP 8.5 scenario is associated with a larger 3-4 o C rise. In 41 addition, we also constructed a range of socio-economic scenarios to investigate the 42 potential impacts of changing population, atmospheric pollution, economic growth and land 43 use change up to the 2050s. Results of INCA simulations indicate increases in mean flows 44 of up to 24%, with flood flows in the monsoon period increasing by up to 27%, but with 45 increasing periods of drought up to 2050. A shift in the timing of the monsoon is also 46 simulated, with a 4 week advance in the onset of monsoon flows on average. Decreases in 47 nitrogen and phosphorus concentrations occur primarily due to flow dilution, but fluxes of 48 these nutrients also increase by 5%, which reflects the changing flow, land use change and 49 population changes. 50

Ten new insights in climate science 2020 – a horizon scan

“…Climate change coupled with socioeconomic drivers can also impact water quality – for instance shifts in monsoon timings can lead to dilution or concentration of nitrogen, phosphorus and other pollutants (Whitehead et al, 2019). Conversely, water quality and pollution levels can impact the ability of sensitive ecosystems such as coral reefs to recover from extreme climate events (MacNeil et al, 2019).…”

Accounting for Multisectoral Dynamics in Supporting Equitable Adaptation Planning: A Case Study on the Rice Agriculture in the Vietnam Mekong Delta

“…Home to over 500 million people (Kuenzer & Renaud, 2012), the world's deltas are critical for economic activities and global food production. Human activities, such as groundwater abstraction, sand mining, and hydropower dam development, have altered the (bio)physical characteristics of deltas through various physical mechanisms including land subsidence, sediment starvation, discharge regime alteration, morphological changes, coastal erosion, and salt intrusion (Minderhoud, Middelkoop, et al., 2020; Renaud et al., 2013; Syvitski et al., 2009; Whitehead et al., 2019). The changes in the (bio)physical character of deltas affect people’s vulnerability in multiple ways: Changing hydrological regimes implies increasing flood hazard; reduced sediment supply means less aggradation of land and decreased soil fertility; coastal erosion and salt intrusion reduce the land’s suitability for various crops, to mention a few.…”

Assessing Land-Cover Effects on Stream Water Quality in Metropolitan Areas Using the Water Quality Index

“…To overcome these limitations, this study presents the first attempt, to our knowledge, to explicitly account for the effects of different land-cover types on the water quality response and key water quality parameters of urban streams. This study was conducted on a national scale, encompassing a wide range of hydromorphological and geographical characteristics and socioeconomic backgrounds, which are also key factors influencing water quality [36][37][38][39][40]. Therefore, this study aimed to provide parameter selection results that are both informative and applicable to other unexplored streams in urban areas of South Korea.…”