Richard Anyah

Simulated Physical Mechanisms Associated with Climate Variability over Lake Victoria Basin in East Africa

Abstract A fully coupled regional climate, 3D lake modeling system is used to investigate the physical mechanisms associated with the multiscale variability of the Lake Victoria basin climate. To examine the relative influence of different processes on the lake basin climate, a suite of model experiments were performed by smoothing topography around the lake basin, altering lake surface characteristics, and reducing or increasing the amount of large-scale moisture advected into the lake region through the four lateral boundaries of the model domain. Simulated monthly mean rainfall over the basin is comparable to the satellite (Tropical Rainfall Measuring Mission) estimates. Peaks between midnight and early morning hours characterize the simulated diurnal variability of rainfall over the four quadrants of the lake, consistent with satellite estimates, although the simulated peaks occur a little earlier. It is evident in the simulations with smoothed topography that the upslope/downslope flow generated by t...

Potential impacts of climate and environmental change on the stored water of Lake Victoria Basin and economic implications

[1] The changing climatic patterns and increasing human population within the Lake Victoria Basin (LVB), together with overexploitation of water for economic activities call for assessment of water management for the entire basin. This study focused on the analysis of a combination of available in situ climate data, Gravity Recovery And Climate Experiment (GRACE), Tropical Rainfall Measuring Mission (TRMM) observations, and high resolution Regional Climate simulations during recent decade(s) to assess the water storage changes within LVB that may be linked to recent climatic variability/changes and anomalies. We employed trend analysis, principal component analysis (PCA), and temporal/spatial correlations to explore the associations and covariability among LVB stored water, rainfall variability, and large-scale forcings associated with El-Nino/Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). Potential economic impacts of human and climate-induced changes in LVB stored water are also explored. Overall, observed in situ rainfall from lake-shore stations showed a modest increasing trend during the recent decades. The dominant patterns of rainfall data from the TRMM satellite estimates suggest that the spatial and temporal distribution of precipitation have not changed much during the period of 1998–2012 over the basin consistent with in situ observations. However, GRACE-derived water storage changes over LVB indicate an average decline of 38.2 mm/yr for 2003–2006, likely due to the extension of the Owen Fall/Nalubale dam, and an increase of 4.5 mm/yr over 2007–2013, likely due to two massive rainfalls in 2006–2007 and 2010–2011. The temporal correlations between rainfall and ENSO/IOD indices during the study period, based on TRMM and model simulations, suggest significant influence of large-scale forcing on LVB rainfall, and thus stored water. The contributions of ENSO and IOD on the amplitude of TRMM-rainfall and GRACE-derived water storage changes, for the period of 2003–2013, are estimated to be ∼2.5 cm and ∼1.5 cm, respectively.

CMIP5 simulated climate conditions of the Greater Horn of Africa (GHA). Part 1: contemporary climate

The present study is a preliminary interrogation of the ability of ten Earth System Models (ESMs) from the fifth phase of coupled model intercomparison project to characterize seasonal and annual mean precipitation cycle over the Greater Horn of Africa region. Each ESM had at least 2 ensemble members. In spite of distributional anomalies of observations, ESM ensemble means were examined on the basis of gridded precipitation data. Majority of the ten ESMs analyzed correctly reproduce the mean seasonal and annual cycle of precipitation for the period 1979–2008 as compared to gridded satellite-derived observations. At the same time our analysis shows significant biases in individual models depending on region and season. Specifically, a modest number of models were able to capture correctly the peaks of bimodal (MAM and OND) and JJAS rainfall while a few either dragged the onset to subsequent months or displaced the locations of seasonal rainfall further north. Nearly all models were in agreement with their representation of the zonal orientation of spatial pattern of the leading EOF rainfall modes; more so, enhanced precipitation over the Indian Ocean and a dipole mode of precipitation pattern are captured in the first and second mode respectively. Further, the corresponding EOF time series of the ESMs rainfall modes were all in phase with observations. However, all models output were positively biased against observations, with large medians and varied range of anomalies. Therefore, caution needs to be taken when choosing models for applications over the region, especially when ensemble means have to be considered.

Multimodel ensemble simulations of present and future climates over West Africa: Impacts of vegetation dynamics

In this study, we take an ensemble modeling approach using the regional climate model RegCM4.3.4-CLM-CN-DV (RCM) to study the impact of including vegetation dynamics on model performance in simulating present-day climate and on future climate projections over West Africa . The ensemble consists of four global climate models (GCMs) as lateral boundary conditions for the RCM, and simulations with both static and dynamic vegetation are conducted. The results demonstrate substantial sensitivity of the simulated precipitation, evapotranspiration and soil moisture to vegetation representation. Although including dynamic vegetation in the model eliminates potential inconsistencies between surface climate and the bioclimatic requirements of the prescribed vegetation, it enhances model biases causing climate drift. For present-day climate, the ensemble average generally outperforms individual members due to cancelation of model biases. For future changes, although the original GCMs project contradicting future rainfall trends over West Africa, the RCMs-produced trends are generally consistent. The multi-model ensemble projects significant decreases of rainfall over a major portion of West Africa and significant increases over eastern North Africa. Projected future changes of evapotranspiration and soil moisture are consistent with those of precipitation, with significant decreases (increases) for western (eastern) Sahel. Accounting for vegetation-climate interactions has localized but significant impacts on projected future changes of precipitation, with a wet signal over a belt of projected increase of woody vegetation cover; the impact on the projected future changes of evapotranspiration and soil moisture over west and central Africa is much more profound. This article is protected by copyright. All rights reserved.

Projecting regional climate and cropland changes using a linked biogeophysical‐socioeconomic modeling framework: 2. Transient dynamics

Understanding climate-cropland interactions and their impact on future projections in West Africa motivated the recent development of a modeling framework that asynchronously couples four models for regional climate, crop growth, socioeconomics, and cropland allocation. This modeling framework can be applied to a future time slice using an equilibrium approach or to a continuous projection using a transient approach. This paper compares the differences between these two approaches, examines the transient dynamics of the system, and evaluates its impact on future projections. During the course of projection up to midcentury, food demand is projected to increase monotonically, while the projected crop yield shows a high degree of temporal dynamics due to strong climate variability. Such temporal dynamics are not accounted for by the equilibrium approach. As a result, the transient approach projects a generally faster future expansion of cropland, with the largest differences over Benin, Burkina Faso, Ghana, Senegal, and Togo. Despite the relative large differences between the two approaches in projecting land cover changes associated with cropland expansion, the projected future climate changes are fairly similar. While the additional cropland expansion in the transient approach favors a wet signal, both the transient and equilibrium approaches project a future decrease of rainfall in the western part of West Africa and an increase in the eastern part. For quantifying climate changes, the equilibrium application of the modeling framework is likely to be sufficient; for assessing climate impact on the agriculture sector and devising mitigation and adaptation strategies, transient dynamics is important. This article is protected by copyright. All rights reserved.

Assessing regional climate simulations of the last 30 years (1982–2012) over Ganges–Brahmaputra–Meghna River Basin

The Ganges–Brahmaputra–Meghna (GBM) River Basin presents a spatially diverse hydrological regime due to it’s complex topography and escalating demand for freshwater resources. This presents a big challenge in applying the current state-of-the-art regional climate models (RCMs) for climate change impact studies in the GBM River Basin. In this study, several RCM simulations generated by RegCM4.4 and PRECIS are assessed for their seasonal and interannual variations, onset/withdrawal of the Indian monsoon, and long-term trends in precipitation and temperature from 1982 to 2012. The results indicate that in general, RegCM4.4 and PRECIS simulations appear to reasonably reproduce the mean seasonal distribution of precipitation and temperature across the GBM River Basin, although the two RCMs are integrated over a different domain size. On average, the RegCM4.4 simulations overestimate monsoon precipitation by

Modelling the impacts of global multi-scale climatic drivers on hydro-climatic extremes (1901–2014) over the Congo basin

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Atmospheric Science for Environmental Scientists

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