Johan Grijsen, Senior Water Resources Specialist for the CDKN-supported project ‘Adaptation to Climate Change in the Hydroelectricity Sector in Nepal’ explores Nepal’s vulnerability to climate change with the help of “Climate Wizard”.

Climate variability and Nepal’s GDP: Current climate variability and extreme events are expected to cause major impacts and economic costs to Nepal’s infrastructure, particularly in such risk domains as agriculture, hydroelectricity and water-induced disasters. In April 2014 the Government of Nepal published a study of the economic impacts of climate change in Nepal, estimating the annual costs of the current climate and water resources variability at 1.5% to 2% of current GDP. These costs are dominated by the often devastating impacts of floods, but also include the impacts of rainfall and runoff variability on agriculture and hydropower. The study – financed by the Climate and Development Knowledge Network (CDKN) - concluded that climate change could exacerbate these impacts, potentially leading to larger costs in the future; hence, the need to dig deeper into the issue of how the future climate of Nepal could look like.

The looming threats of climate change: Hydropower plants in Nepal are mostly run-of-river (R-o-R) installations and are thus severely affected by the huge seasonal variations in river flows. Flows are abundant during the monsoon season (June to September/October), but low flows occur during the remainder of the year, particularly during the winter season from Decemberwell into April. While much of the hydropower potential of the country remains as yet undeveloped, insufficient generation capacity during the winter season leads to frequent load shedding and high associated economic costs from unmet electricity demands. Would climate change add insult to this injury?

Equally worrying is that the longevity of hydropower plants is threatened by precipitation-induced natural disasters, notably floods, landslides, and severe erosion and sedimentation problems associated with the summer monsoon. And then there is the increasing risk of Glacial Lake Outburst Floods (GLOFs) due to accelerated glacier melt caused by increasing temperatures and the subsequent retreat of glaciers. It is these threats that scientists fear may increase in the future due to an increasing variability of precipitation and increasing temperatures.

Searching for evidence: As a follow-up to the previous study,CDKN commissioned early 2015 the study ‘Adaptation to Climate Change in the Hydroelectricity Sector in Nepal’, led by the Nepal Development Research Institute (NDRI). This new study aims inter alia to develop a solid evidence base on the vulnerability of the hydroelectricity sector to climate change, identify viable adaptation options, mainstream climate adaptation and build adaptation capacity in the sector.This blog looks into the drivers of hydrological change and variability. We examine the question how the future precipitation and temperature regime of Nepal could change, particularly across the northern medium to high altitude region of Nepal, which provides most of the hydropower potential for the country.

The Climate Wizard:The International Center for Tropical Agriculture (CIAT) operates the Climate Wizard (CW) tool[1], which was initially developed to provide easy access to climate projections provided by a large ensemble of Global Climate Models (GCM), with multiple climate projections prepared under the Coupled Model Inter-comparison Project phase 3 (CMIP3). Using the output of the latest CMIP5, this tool is now being updated and revamped[2] for 23 GCMs and two Representative Pathway Concentration scenarios (RCP4.5 and RCP8.5), thus providing 46 bias-corrected climate projections for the 21st century for user defined areas (at a 50 km grid resolution).

Typically the Climate Wizard provides multiple statistically downscaled and bias-corrected projections of long-term average changes in monthly and annual precipitation, temperature and potential evapotranspiration for multiple time horizons. Projections for shorter time intervals relevant to extreme events can also be generated. Statistical representations of modeled future climate projections are best achieved by examining a range of time rather that a single year; for example the time period 2041-2060 is often considered to be representative for the mid-century (2050). It is generally assumed that each GCM could well represent the future climate on earth. It is thus crucial to not only analyze the projections of one GCM for one selected emission scenario, but to use instead ensemble analysis. This combines the projections of many GCMs for multiple future scenarios and attempts to quantify the range of possibilities for future climates.

What Global Climate Models andthe Climate Wizard have to say about Nepal’s future climate:Here we focus on how climate change could impact hydro-energy generation in the middle to high altitude regions of Nepal.In order words,we examine how climate change could impact monsoon runoff as well as winter runoff. In a later blog we will address possible climate change impacts on extreme events like floods, GLOFs, etcetera.

Higher temperatures and receding glaciers: Figure 1 reflects how annual average temperatures and precipitation could change by 2050 across the North-West (1), North-Central (3) and North-East (5) regions of Nepal under RCP4.5 (red markers) and RCP8.5 (black markers). Projected temperature changes (vertical axis) range from 1.5 to 40C under RCP4.5 and from 2 to 50C under RCP8.5, on average about 30C, well above the 20C increase found as an average projected temperature increase for many other regions in the world. Detailed investigation of all available projections for Nepal revealed further that the Northern higher altitudes regions are expected to warm-up 0.50C more than the Southern lower altitudes regions and that across Nepal winters are projected to warm-up 0.50C more than summers.

[caption id="attachment_56039" align="aligncenter" width="600"] Projected climate changes for the Northern regions of Nepal, for 2050[/caption]

Undoubtedly, these findings suggest with high confidence that in the future snow melt may start earlier than today and that glacier melt will increase as well.  This would provide for the time being a welcome increase in runoff during particularly April and May, until such time that glaciers have retreated far enough to no longer produce extra spring season runoff. The risk of GLOFs could also increase due to additional glacier melt. However, rising temperatures would as such not significantly augment nor decrease the already critically low winter flows, nor would they significantly affect hydro-energy generation during the winter season.

Wetter monsoons may induce slightly higher winter runoff and hydro-energy generation: Six out of seven GCM model runs project higher monsoon rainfall, as can also be seen along the horizontal axis in Figure 1. Higher precipitation generates higher monsoon runoff, but higher summer temperatures cause some flow reduction due to higher evaporation. On balance, two out of three climate projections would indicate the probability of a higher monsoon runoff.But, since the country already enjoys an abundance of monsoon runoff, this would generally not lead to an increase in generated summer hydro-energy. Instead, extra erosion and sediment loaddue to increased precipitation could lead to some extra downtime of the power plants. The good news is though that higher monsoon precipitation and runoff would also induce a slightly higher base flow runoff during the period November to March. In turn that would slightly increase the generated hydro-energy during the critical winter season.

To contact the author of this blog, please write to: Johan Grijsen, Sr. Water Resources Specialist, Member of the Study Team, johangrijsen@yahoo.com; for further information on project activities, please contact Divas B. Basnyat, Team Leader, NDRI, divas@ndri.org.np, Telephone: +977-1-5537362, 5554975.

[1]Data source: http://climatewizard.ciat.cgiar.org/; Global Climate Model (GCM) output from the World Climate Research Program's (WCRP) Coupled Model Inter-comparison Project phase 5 (CMIP5) multi-model dataset; sponsored by theUniversity of Washington, the University of Southern Mississippi, Santa Clara University, the World Bank and the Nature Conservancy.

[2] Results for CMIP5 are not yet publicly available on the Climate Wizard, but were provided to NDRI through the kind cooperation of Evan Girvetz of CIAT

Occasionally, CDKN invites guest bloggers from around the world to contribute their views on cdkn.org The views expressed here do not necessarily represent those of CDKN or its Alliance members.

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