PRECIPITATION PREDICTION & HYDROPOWER

Published: December 17, 2015

Precipitation

 

In the face of climate change, how crucial is precipitation prediction to Hydropower generation? Working with scientists and research bodies, experts in Germany explore modelling as a means to critically assess the impacts of a changing hydrologic regime on future energy generation.

WHY PRECIPITATION PREDICTION IS CRUCIAL FOR TOMORROW’S ENERGY

Hydroelectricity is a clean power resource harnessing the natural potential energy of water. Its generation is directly controlled by run-off which is in turn dependent on precipitation. While the extent of future global climate change is uncertain, this has an impact on power generation. Read more.

UNPREDICTABLE CLIMATE CHANGE PREDICTION

The development of “crystal-ball” methodologies to investigate impacts of climate change on hydropower production has begun. An overview of a recent thesis, based on two Asian high-altitude river basins in the Himalaya-Karakoram-Hindu Kush mountain ranges, demonstrates the promise and the challenges faced in incorporating climate change into the design parameters of hydropower projects. Read more.

 

“Evident evolutions in our planet’s weather and hydrologic patterns require that we, as consultants and hydro-sector players, need to incorporate climate change prediction in most, if not all new hydropower projects. But we also need to apply a sound engineering judgement to counterbalance the  limitations of modelling capabilities.”

Berhon Dibrani – Civil and Water Resources Engineer – Lahmeyer International


WHY PRECIPITATION PREDICTION IS CRUCIAL FOR TOMORROW’S ENERGY

 

CHANGING CONDITIONS

In the past century, only a small increasing trend of global river discharge has been observed, yet, for funding agencies , owners and operators in the hydropower sector, the fact that this will change is an important question that needs to be answered.

On the one hand, predicted temperature and precipitation changes will alter the hydrological characteristics of river catchments, resulting in changes in river flow. On the other, warmer temperatures may lead to an increase in evaporation, which in turn increases the moisture content of the atmosphere resulting in a more favourable formation of clouds and precipitation. Moreover, it is likely that climate change will also have an impact on land use and land cover – changes affecting the hydrological characteristics of a river basin that must be taken into account as well.

With no global guarantee of what the changes will be where and when, the impacts of climate change are too complex to allow general statements on a regional hydrology. The run-off regime for each hydropower project therefore requires an individual assessment of potential future conditions and site specific analysis for individual power stations is required to ensure the adaptation of designs to be able to cope, if needed, with changing conditions.

Berhon Dibrani

Berhon Dibrani

THE WORK HAS ALREADY BEGUN

Given its many years of designing Hydropower plants, all around the world and in very different conditions, Lahmeyer International is no stranger to the need to take into consideration the unique geological, environmental and hydrological circumstances of individual station sites. These include all potential changes of the hydrologic regime and the potential impacts and risks that an installation may be required to cope with over a long period of time. In more recent years, it has seen its clients growing increasingly concerned about the less predictable, future uncertainties in their projects. Resulting in an elevated demand for climate change studies, including impact assessments and adaptation strategies, so Lahmeyer’s efforts to develop an even more detailed outlook have increased.

Today “crystal-ball” precipitation predictions are closer than many think…


UNPREDICTABLE CLIMATE CHANGE PREDICTION

The two projects studied are located in Nepal (Upper Tamakoshi Hydropower Plant – currently under construction) and one in Pakistan (Diamer Basha Hydropower Plant – planning stage). The location of the two study area, namely the Upper Tamakoshi Basin in Nepal (UTB) and the Upper Indus Basin in Pakistan (UIB) are located in the figure below.

Climate Prediction UIB UTB

CHALLENGE 1- AVAILABILITY OF DATA

Rainfall stations are usually sparsely distributed in remote areas as was the case here. This was further complicated by the fact that that these trans-boundary river basins extend into countries from which no data was readily available, i.e.  China – UTB and China, Afghanistan, Tajikistan and India – UIB.

Therefore, daily precipitation data from the Asia Precipitation-Highly Resolved Observational Data Integration towards Evaluation of the Water Resources (APHRODITE) project were applied for the project areas from 1951-2007 with a grid resolution of 0.25°. The gridded precipitation data set was created by interpolating rain-gauge observations obtained from over 5,000 meteorological and hydrological stations across Asia.

CHALLENGE 2- THE SPATIAL RESOLUTION OF CLIMATE MODEL RESULTS

Historical and future Regional Climate Model (RCM) outputs were applied, which were dynamically downscaled from Global Circulation Model (GCM) outputs. The primary advantage being RCM have a significantly higher spatial resolution of 10 to 50 km in contrast to a GCM at 100 to 300 km.

The outputs from the following four Regional Climate Models were selected:

(1) CCLM (Consortium for Small-Scale Modelling Climate Local Model) with a resolution of 0.25° driven by the general circulation model ECHAM5.

(2) CCLM with a resolution of 0.44° driven by the general circulation model ECHAM6.

(ECHAM5 and ECHAM6 were developed at the Max Planck Institute in Germany).

(3) RCA4-RCM by the Rossby Centre of the Swedish Meteorological and Hydrological Institute using the Earth System Model EC-Earth as General Circulation Model

(4) RegCM4 model-run performed by the Centre for Climate Change Research of the Indian Institute of Tropical Meteorology based on the LMD General Circulation Model.

All Global Circulation Models and Regional Climate Models, including those selected, contain systematic uncertainties based on physics, parameterizations and due to larger scale patterns. These systematic occurring biases require a correction based on available data during a base period. Future projections of precipitation and temperature were then bias-corrected the same way, assuming that the correction parameters, which are established during the base-period, are also valid for future periods. As an example, the figure below shows on the left panel the raw model outputs during the base period 1976 to 2005 and on the right panel bias-corrected results.

Climate Prediction Corrections

CHALLENGE 3 – THE PREDICTION OF FUTURE GLACIAL MELT-OFF

This is especially relevant to flows of the Upper Indus River, which are mainly determined by the contribution of snow and glacier melt water during the warm season. Assuming a constant glacier size during the simulation period, the mean annual discharge grows significantly in response to increasing glacier melt-water contributions. However, the volume of the large Asian glaciers has not been determined in sufficient detail to estimate when flows start to decrease due to a reduced size.

RESULTS OF THE STUDY

With the application of a hydrological model and a reservoir operation model, the energy generation of both hydropower plants were estimated.

For the Diamer Basha Hydropower Plant in Pakistan, projections predict a positive trend in mean annual discharge and thus an increase in energy generation, between 1% and 11% until 2100.

Basha Hydropower Plant

At the Upper Tamakoshi Hydropower Plant in Nepal, evidence suggests that the electricity generation will only change marginally in the future, between 1% and 5% until 2100.

Tamakoshi Hydropower Plant

SOME UNCERTAINTIES REMAIN

As important as the complex computations that led to the above results is the appreciation and assessment of the major uncertainties involved:

  • Uncertainties from Observational Data

As a consequence of  few (Upper Indus Basin), or none (Upper Tamakoshi Basin) observational stations located in the basins studied, the interpolated APHRODITE data and particularly the precipitation values contain errors, carried forward through the bias correction and the calibration process.

  • Uncertainties from Climate Model Simulations

In general, physical processes happening on Earth are represented in a simplified form in models, resulting in strong approximations or systematic errors. Unknown population and economic developments lead to unknown future greenhouse gas emission levels which strongly regulate the global climate. Future projections of regional precipitation patterns in orographic complex areas are still very uncertain.

  • Uncertainties from Hydrological Model

The values needed as input for run-off modelling are predominately determined using GIS data, which again contains errors. Further restrictions result from the fact that model parameters are kept constant when it is likely that climate change will also alter basin characteristics (e.g. land use and land cover).

  • Uncertainties from Glaciers

Reliable river flow projections in the respective catchment areas require knowledge of future glacier developments, but as no accurate data on the current and the future extent (area/volume) of the glaciers and mass balances exist, this represents a strong uncertainty.

“In conclusion, evident evolutions in our planet’s weather patterns require that we, as consultants and hydro-sector players, need to incorporate climate change prediction in most, if not all new hydropower projects. But we also need to apply a sound engineering judgement to counterbalance the limitations of modelling capabilities.”

Berhon Dibrani – Civil and Water Resources Engineer, Lahmeyer International

Due thanks to the Institute for Atmospheric and Environmental Sciences of the Goethe University of Frankfurt and theses participants for the use of this study example.

Shared insights

The question also impacts many other sectors; irrigation, environment, social infrastructure… In a combined effort with the Institute of Meteorology and Climate research from the Karlsruhe Institute for Technology (KIT), Lahmeyer holds regular seminars to heighten awareness and share, where it is possible, methods and solutions to colleague and customer concerns.

CO-ADVISING

Further expanding knowledge of trends, methodologies and models related to climate change prediction, a collaboration with the Institute for Atmospheric and Environmental Sciences of the Goethe University of Frankfurt sees experts co-advising on Master’s theses related to future changes in precipitation and the potential impacts of Climate Change on hydropower generation.

More information

Berhon Dibrani – Civil and Water Resources Engineer – Lahmeyer International

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