Development of high spatial resolution rainfall data for Ghana

Abstract

Various sectors of the country's economy – agriculture, health, energy, among others – largely depend on climate information, hence availability of quality climate data is very essential for climate‐impact studies in these sectors. In this paper, a monthly rainfall database (GMet v1.0) has been developed at a 0.5° × 0.5° spatial resolution, from 113 Ghana Meteorological Agency (GMet) gauge network distributed across the four agro‐ecological zones of Ghana, and spanning a 23‐year period (1990–2012). The datasets were first homogenized with quantile‐matching adjustments and thereafter, gridded at a spatial resolution of 0.5° × 0.5° using Minimum Surface Curvature with tensioning parameter, allowing for comprehensive spatial fields assessment on the developed dataset. Afterwards, point‐pixel validation was performed using GMet v1.0 against gauge data from stations that were earlier excluded due to large datagaps. This proved the reliability of GMet v1.0, with high and statistically significant correlations at 99% confidence level, and relatively low biases and rmse. Furthermore, GMet v1.0 was compared with GPCC and TRMM rainfall estimates, with both products found to adequately mimick GMet v1.0, with high correlations which are significant at 99% confidence level, low biases and rmse. In addition, the ratio of 90th – percentile provided fairly similar capture of extremes by both TRMM and GPCC, in relation to GMet v1.0. Finally, based on annual rainfall totals and monthly variability, k‐means cluster analysis was performed on GMet v1.0, which delineated the country into four distinct climatic zones. The developed rainfall data, when officially released, will be a useful product for climate impact and further rainfall validation studies in Ghana.

Assessment of Long-Term Spatio-Temporal Rainfall Variability over Ghana using Wavelet Analysis

“…Rainfall values begin to increase from about 60 mm in the north to as high as 200 mm in the south, especially towards the southwestern part of the country. This is shown in Figure 9b) and can also be found in [30,51].…”

“…The Savannah Zone interestingly records high values between 160 and 200 mm during this period. The effect of the Volta basin on the local climate is significantly seen around Kete Krachi (7.8 • N and 0.02 • W) in this period with rainfall values between 180-200 mm (Figure 9c) [30,51].…”

“…That validation was however performed using only fourteen gauges from meteorological stations in Ghana instead of a gridded data. With the current availability of GMet gridded data by Aryee [30] which was computed using 113 stations, it has become necessary to compare the two gridded datasets to ensure the reliability of the GPCC data. The comparison between GMet gridded data and GPCC data is presented and discussed.…”

“…The strength of the Monsoon winds therefore begins to weaken. The ITD begins to return and hence resulting in this minor rainy season [30,51].…”

“…The GMet data used for the validation is a gridded data [30], collected from a total of 113 stations including all the synoptic, climatological and agro-meteorological stations in Ghana with less than 10 % data gap and covering the period of 1980-2012 ( Figure 1). The data was first reconstructed using the Regularized Expectation Maximization (RegEM) algorithm described in Schneider [31] to estimate all missing data.…”