Going local: Evaluating and regionalizing a global hydrological model’s simulation of river flows in a medium-sized East African basin

https://doi.org/10.1016/j.ejrh.2018.10.007Get rights and content
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Highlights

  • We examine the performance of a global land surface model for a local application.

  • Without modification the global model only provides an approximation of river flow.

  • Rainfall correction and enhancing runoff delay are essential changes.

  • We show irrigation is necessary to explain a drying trend in a key Rufiji tributary.

Abstract

Study region

The Rufiji basin, East Africa.

Study focus

Rapid advances in global hydrological model (GHM) resolution, model features, and in situ and remotely sensed datasets are driving progress towards local relevance and application. Despite their increasing use, however, evaluation of local hydrological performance of GHMs is rare. In this paper, we examine the performance of a well-known GHM (LPJmL, recently modified to ∼9 km resolution) with and without modest steps to regionalise the model. We consider the Rufiji river basin, an economically important medium-size basin in eastern Africa.

New hydrological insights for the region

Our results indicate that the unmodified GHM does provide a reasonable first approximation of spatial variability in mean flow conditions, but scores rather poorly on seasonal and inter-annual variability. For the model to achieve levels of performance indicators comparable with bespoke modelling, modifications to model inputs, additional runoff delay and wetland parameterization were required. The largest improvements are associated with adjustments in precipitation and enhanced runoff delay. With the modified version, as a proof of concept, we show that a well-known drying trend in a major tributary of the Rufiji can be explained by implementing irrigation abstractions in the model. Overall, the results suggest that with limited and fairly simple modification GHMs can be regionalised to allow their use for scenario testing and further exploration of key local processes in basins with limited observational data.

Keywords

LPJmL
Global hydrological model
Regionalization
Rufiji
Irrigation abstractions
Water resources
Stiegler’s Gorge

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