Rainfall studies for the highlands of Eritrea

[摘要] English: Long-term rainfall records of the highlands of Eritrea were examined to reveal the short andlong-term patterns. Monthly and annual spectra have been analysed to provide apreliminary assessment in terms of homogeneity, spell length, water balance, drought andspatial variability.Three methods of spatial interpolation were evaluated for mapping continuous spatialrainfall values for mean annual rainfall totals. Interpolation methods examined in thisstudy include inverse distance weighted (!DW), Spline and Kriging. A statistical assessmentof the continuous surface created indicates that there is little difference between theestimating ability of the three spatial interpolation methods, but with Kriging performingbetter overall than Spline or !DW.Monthly means provide little information on many properties of the rainfall that are relevantto the wide variety of rainfall-related activities and decision making. A stochastic rainfallgenerator model based on a first-order Markov chain was developed for generation ofartificial daily rainfall data from monthly totals. Intensive statistical testing of theperformance of the model reveals that the model can be used with confidence to generate apseudo daily rainfall dataset for the peak rainy months (July-August), for the highlands ofEritrea.A deterministic model was developed to investigate how the global rainfall predictorscorrelate to the two peak rainy months (July-August), which contribute 65% of the totalrainfall in the highlands of Eritrea. The main aim of looking at these relationships is todevelop a simple statistical model for forecasting rainfall amount. In a preliminary step, inorder to identify the most influential rainfall predictor a correlation matrix and stepwiseregression of 11 predictors with different lags were analysed. The influence of the southernIndian Ocean Sea Surface Temperatures was identified as the most influential predictor forthe highland of Eritrea. The model was validated using the jack-knife skill test, Chi-squaredand deviation based test giving a promising result.

[发布机构] University of the Free State