Multi-site stochastic modelling of daily rainfall in Uganda

Abstract

The availability of precipitation records in Uganda has significantly decreased since the 1970s, severely limiting the data available for hydrological modelling. This problem has been addressed in this study by using the generalized linear modelling (GLM) framework to develop stochastic daily rainfall models that have the capability for extending and infilling historic data sets. We have used a relatively sparse raingauge network in the Kyoga basin (in the Upper Nile) to reproduce spatial and temporal patterns of precipitation by fitting occurrence (logistic) and amounts (gamma) models as functions of dominant seasonal, climate and geographical controls. The GLMs were able to reproduce rainfall properties when predefined climatic zones are modelled independently. We were not able to represent the spatial variability of the equatorial climate with one integrated basin scale model, however this is not thought to preclude application to basin scale hydrological modelling.Key words generalized linear models; rainfall; stochastic models; climate change; Uganda; Kyoga; ENSO Modélisation stochastique multi-sites de la pluie journalière en Ouganda Résumé La disponibilité des données de précipitations en Ouganda a considérablement diminué depuis les années 1970, limitant fortement les données disponibles pour la modélisation hydrologique. Ce problème a été abordé dans cette étude dans le cadre de la modélisation linéaire généralisée (MLG), afin de développer des modèles stochastiques de pluie journalière qui puissent étendre et compléter les données historiques. Nous avons utilisé un réseau de pluviomètres de relativement faible densité dans le bassin du Kyoga (dans le Nil Supérieur), afin de reproduire les patrons spatiaux et temporels des précipitations en modélisant l'occurence (logistique) et les volumes (gamma) comme fonctions des forçages dominants saisonniers, climatiques et géographiques. Les MLG sont en mesure de reproduire les propriétés des pluies lorsque des zones climatiques pré-définies sont modélisées de façon indépendante. Nous n'avons pas pu représenter la variabilité spatiale du climat équatorial avec un modèle à l'échelle intégrée du bassin, cependant ceci ne semble pas devoir empêcher la mise en oeuvre d'une modélisation hydrologique à l'échelle du bassin.

Rainfall and temperature estimation for a data sparse region

“…Parameters may also be conditioned in time using slowly varying climate indices to replicate low-frequency persistence (Wilby et al, 2002), or in space using predefined climatic zones to condition spatial variability across large (tropical) river basins (e.g. Kigobe et al, 2011). We extended these approaches by interpolating weather generator parameters conditional on point terrain and remotely sensed indices (precipitation and vegetation).…”

A modular class of multisite monthly rainfall generators for water resource management and impact studies

“…Since the effect of low frequency climatic mechanisms can be more evident in low frequency (monthly/annual) rainfall series, it can be worth including climatic indices (as well as other non-climatic covariates) in the modelling framework as proxies of the physics of the underlying processes. In daily rainfall analysis this task has been usually accomplished by allowing the rainfall distribution parameters to vary with covariates through the Generalized Linear Models (GLM; Coe and Stern, 1982;Chandler and Wheater, 2002;Yang et al, 2005;Segond et al, 2006Segond et al, , 2007Furrer and Katz, 2007;Kigobe et al, 2011;Kleiber et al, 2012) or their generalisations, such as the Vector GLM (VGLM; Yee and Wild, 1996;Yee and Stephenson, 2007;Maraun et al, 2010).…”

The water balance of Lake Kyoga, Uganda

“…A reasonable number of rainfall records are available in the Kyoga basin (Kigobe et al 2011), and longterm monthly records provide a basis for estimating the input to the basin. Twenty stations are available from the 1996 study of the hydroelectric potential of the Nile in Uganda (Gibb 1996), which included a preliminary estimate of the contribution of the Kyoga basin.…”