Rainfall studies for the highlands of Eritrea

English: Long-term rainfall records of the highlands of Eritrea were examined to reveal the short and long-term patterns. Monthly and annual spectra have been analysed to provide a preliminary assessment in terms of homogeneity, spell length, water balance, drought and spatial variability. Three methods of spatial interpolation were evaluated for mapping continuous spatial rainfall values for mean annual rainfall totals. Interpolation methods examined in this study include inverse distance weighted (!DW), Spline and Kriging. A statistical assessment of the continuous surface created indicates that there is little difference between the estimating ability of the three spatial interpolation methods, but with Kriging performing better overall than Spline or !DW. Monthly means provide little information on many properties of the rainfall that are relevant to the wide variety of rainfall-related activities and decision making. A stochastic rainfall generator model based on a first-order Markov chain was developed for generation of artificial daily rainfall data from monthly totals. Intensive statistical testing of the performance of the model reveals that the model can be used with confidence to generate a pseudo daily rainfall dataset for the peak rainy months (July-August), for the highlands of Eritrea. A deterministic model was developed to investigate how the global rainfall predictors correlate to the two peak rainy months (July-August), which contribute 65% of the total rainfall in the highlands of Eritrea. The main aim of looking at these relationships is to develop a simple statistical model for forecasting rainfall amount. In a preliminary step, in order to identify the most influential rainfall predictor a correlation matrix and stepwise regression of 11 predictors with different lags were analysed. The influence of the southern Indian Ocean Sea Surface Temperatures was identified as the most influential predictor for the highland of Eritrea. The model was validated using the jack-knife skill test, Chi-squared and deviation based test giving a promising result.