Paper Example on Rainfall: Critical to Global Hydrology and African Economies

Rainfall plays an essential role in the global hydrological cycle and has significant socio-economic impacts (Varikoden et al. 2012). Many countries have been affected by rainfall variability and longterm changes in both rainfall amounts and distribution over recent decades (Christian, 2016). Rainfall is the backbone of many agricultural activities across the world, more so for African countries. Agriculture forms an important role of the economies of all African countries. Agriculture is also important in achieving continental priorities of making Africa great such as, eliminating poverty and hunger, improving trade between African countries and empowering industrialization. Agriculture is crucial for most developing countries in Africa including Ghana because, it is the main source of food, and is a source of income for most of the population in rural settings. According to FAO (2019), agriculture accounts for 39.4% of the GDP of most developing countries (Rossi et al., 2017). It is therefore important for such countries to have water resources information for weather forecasting, identifying recent rainfall events and how they might change during the rainy seasons, and countries preparedness to rainfall variations.

Is your time best spent reading someone else’s essay? Get a 100% original essay FROM A CERTIFIED WRITER!

Save 25%

Rain gauges have been used for a long time to provide rainfall information (Khodadoust Siuki et al., 2016). However, Africa has one of the sparsest rain gauge networks globally, which by observations have declined significantly in the past 20 years. The African gauge network is associated not only with sparse measurements, but with many gaps in the time-series which degrade the quality of the information available from rain gauges.

Rainfall plays a significant role in the developing countries of sub-Saharan because these countries mainly depend on rain for agricultural production (Mahuni, 2016). Also, since agriculture is the backbone for most West African countries and Africa at large, there have been many concerns about the global climate change trends (Nouaceur and Murarescu, 2020). These changes lead to extreme rainfall conditions where some parts receive too much rainfall that cause floods, while others experience very little that leads to drought and famine (Mahuni, 2016). Ghana, as a country in West Africa, is not an exception to these changes.

Due to development in remote sensing technologies, other means of measuring rainfall through satellite imagery have emerged that can provide extremely valuable information about rainfall in the absence of adequate rain gauge data (Hiroshima, 1999). This improved method provides additional information, such as land cover, temperature variations, evaporation rates, precipitation, and soil moisture content (Wang et al., 2017). While some ground-based radars are in use across Africa, many are not completely operational due to high costs in maintaining them. As such, they are currently not practical for operational use across Africa (Chave et al., 2019). Satellite estimates can be obtained through, infrared data (IR) by linking cloud-top temperature or reflectivity to rain rates through empirical relationships. Another advanced method has been introduced that uses passive microwave sensors (PMW) that detects the radiation from hygrometers and link this to rainfall rates. These methods provide a more direct interpretation of precipitation. In recent years, a lot of modifications have been made in satellite rainfall estimation – in part due to more advanced sensors on board satellites. Satellite estimates are only estimates at the end of day and therefore they have biases and uncertainties that need understanding. Current satellite rainfall estimates typically possess good potential in rainfall estimation, even at relatively short time-steps (e.g. less than 10 days) [REFS].

Motivation

Many sources show that West Africa is one of the world's regions that experiences heavy rainfall annually. Unlike other areas experiencing a fluctuating amount of Rainfall, West Africa has been receiving continuously adequate rain (Pugh 2019). However, in the past few years, the country has been reported to experience extreme rainfall conditions whereby unpredicted floods have been experienced as well as drought (Pugh 2019). This has been a concern to the local weather experts in Ghana and the TAMSAT that uses a satellite to monitor weather between the tropics. All these bodies come up with reports about the extreme rainfall conditions (Brown et al., 2017). Given the lack of rain gauges and the availability of satellite estimates, there is a need to analyze the extreme rainfall conditions in Ghana from TAMSAT estimates using existing rain gauge estimates from local meteorological stations.

Objectives

The aim of this dissertation is to evaluate the performance of the Tropical Applications of Meteorology using Satellite and other data (TAMSAT) satellite rainfall dataset. TAMSAT improves the capacity of Africa metrological agencies and other organization by providing and supporting the use of satellite-based rainfall estimates and other associated data products (Maidment et al., 2017). TAMSAT data is preferred over other available satellite products listed below due to the following advantages.

• Long-time series.
• Short latency.
• Short-time steps.

The objective of this dissertation can be summarized as follows:

• A better understanding of how TAMSAT rainfall estimates capture Ghana’s rainfall climate.
• An analysis of how TAMSAT rainfall estimates capture extreme rainfall events over Ghana.
• So, to achieve the above aims, this project was guided by the following questions:
• Do TAMSAT rainfall estimates capture the temporal and spatial patterns of Ghana’s rainfall climate?
• What is the observed occurrence of extreme rainfall events?
• For a given threshold in TAMSAT rainfall, what is the probability of observing an extreme rainfall event?
• How do other widely used satellite products capture extreme rainfall events?

Study Area

Ghana is a country that is in the West of the African continent. It is located along the Gulf of Guinea and the Atlantic Ocean. The country borders Togo in the East, Burkina Faso on the North, Ivory Coast on the West, and the Atlantic Ocean on the South (Segbefia et al., 2018). The country is found a few degrees on the North of the Equator, which means it is a warm country. Ghana is located between longitude 1015’ E and 3015 W and Latitude 4045’N and 110 N. the famous prime meridian passes through Ghana at the port of Tema.

Four ecological zones in Ghana have been defined for the purpose of the evaluation: Coastal, Forest, Transition and Savannah regions. These ecological zones were selected based on the density of gauging stations, geographical location and the seasonal rainfall regime.

Dissertation Outline

This project will start by reviewing the literature on climatology of West Africa as a region, Ghana’s rainfall climate and observed and projected extreme rainfall events. This will be followed by a description of the data used in the analysis. The various validation statistics and approaches used to analyse the data will be explained and this will be followed by the comparison between rain gauge measurements and TAMSAT rainfall estimates before analysing extreme rainfall events using both gauge data and TAMSAT estimates. Then, discussion of the results will be done, and this will be followed by conclusions and recommendations.

Literature Review

Rainfall climatology studies for Ghana and other African countries based on gauge data.

African countries are vulnerable in cases of rainfall variations and fluctuation during different seasons. Therefore, real-time monitoring of rain is crucial (Maidment et al., 2012). The information obtained can be used in warning the farmers of any probable crop shortfall in areas that occasionally experience drought. This was an observation made by Maidment, Grimes, and Rojas while investigating satellite-based and model re-analysis rainfall estimates for Uganda (Maidment et al. 2012). The countries are, however, faced with the challenge of depending on ground-based observations, which are faced with various challenges that make the data obtained unreliable. Yet, this gap can be filled through data collected from satellite-based methods such as numerical models and algorithms. The plans will, however, require critical analysis to come up with applicable and usable data. In their studies, they used three satellite products, two numerical models, and a network of twenty-seven rain gauges. Rainy season from February to June was considered for a period of four years from 2001 to 2005. The three satellite products used exhibited comparable traits that can be used in rainfall estimates.

Satellite rainfall estimates studies for Ghana and other African Countries.

It is necessary for a country to have reliable data sources that will be used to analyze various seasons. Anita Asadullah, Neil Mcintyre, and Max Kigobe evaluated five satellite products (TRMM, CMORPH (Climate Prediction Center MORPHing technique), TAMSAT, RFE (Recursive Feature Elimination) and PERSIANN) for the approximation of rainfall in Uganda in East Africa. The research made use of five satellite-based algorithms for the estimation of rainfall alongside historical rainfall data that was obtained from rain gauges in four regions of Uganda. The focus of the research was to analyze the differences between the products as well as the accuracy in estimating rainfall.

According to Mircea Grecu and William S. Olson, precipitation retrievals from satellite combined radar and radiometer observations approaches of estimation are faced with various challenges. The two approaches are based on optimal estimation theory. Regardless of the procedure used to address the optimization problem, other challenges, such as the mismatch between the two methods of estimation and mathematical errors, need to be addressed. In their article, the two researchers used Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Mission (GPM) algorithm approaches to mitigate the challenges. In addition to that, they availed suggestions and potential solutions to the identified problems. The main difficulty in obtaining Path Integration Attenuation estimates derived from satellite radiometer observations is that low-frequency radiometer stations are higher than space-born radars. Regardless of the inconsistencies between the frequencies, the estimation of rainfall information from satellite combined radar and radiometer observations is a topic that has attracted researches in recent years because of the associated benefits that the combined approaches for the advances of satellite radiometer rainfall estimation algorithms. The information obtained...