Climate Change and Pastoral Economy in Kenya:A Blinking Future

Abstract: The present paper examines the changing climatic scenarios and associated effects on livestock farming (pastoralism) in the arid and semi arid lands (ASAL) of Kenya, which cover over 80% of the country. The study was carried out in the semi arid Mukogodo Division of Laikipia District in Kenya. This division received a mean annual rainfall of approximately 507.8?mm and the main source of livelihood was pastoralism. Questionnaire, structured interview, observation and literature review were the main methods of data collection. Rainfall was used in delineating changes in climate. Standardized precipitation index (SPI) and Markov process were used in analyzing drought severity and persistence, respectively. Approximately 38% of all droughts between 1975 and 2005 were prolonged and extremely severe, with cumulative severity indices ranging between ?2.54 and ?6.49. The probability that normal climatic conditions persisted for two or more consecutive years in Mukogodo Division remained constant at approximately 52%. However, the probability of wet years persisting for two or more years showed a declining trend, while persistence of dry years increased with duration. A drying climatic trend was established. This drying trend in the area led to increased land degradation and encroachment of invasive nonpalatable bushes. The net effect on pastoralism was large-scale livestock loss through starvation, disease and cattle rustling. Proper drought monitoring and accurate forecasts, community participation in all government interventions, infrastructural development in the ASAL and allocation of adequate resources for livestock development are some of the measures necessary for mitigating the dwindling pastoral economy in Kenya and other parts of the world.     

Heat extraction from aquifer geothermal systems

This study aims to model temperature distributions in an aquifer thermal extraction (ATE) system that contains a single extraction well in a thin confined aquifer. The aquifer is bounded by hot dry rocks with different thermomechanical properties and thicknesses. Based on the heat convection–conduction equation, a mathematical model is developed to describe the spatial and temporal temperature distributions of the ATE systems. The mechanisms of heat transfer in the model involve horizontal convection and thermal conduction in the aquifer, and vertical thermal conduction in both rocks. A semi‐analytical solution in dimensionless form is developed using the Laplace transform technique and its corresponding time‐domain result is computed by the modified Crump method. In addition, the steady‐state solution is obtained by applying the final value theorem. The simulation results from the semi‐analytical solution indicate that the aquifer temperature distributions are affected by aquifer thickness, the thermomechanical properties of the aquifer and rocks, geothermal gradient, outer boundary temperatures of the rocks, extraction rate, and operating time. The present solution can be used as a preliminary tool for assessing heat extraction efficiency in ATE systems. Copyright © 2010 John Wiley & Sons, Ltd.     

Parameterizing canopy resistance using mechanistic and semi‐empirical estimates of hourly evapotranspiration: critical evaluation for irrigated crops in the Mediterranean

In this paper two models are presented for calculating the hourly evapotranspiration λE (W m^?2) using the Penman–Monteith equation. These models were tested on four irrigated crops (grass, soya bean, sweet sorghum and vineyard), with heights between 0·1 and 2·2 m at the adult growth stage. In the first model (Katerji N, Perrier A. 1983. Modélisation de l'évapotranspiration réelle ETR d'une parcelle de luzerne : rôle d'un coefficient cultural. Agronomie 3(6): 513–521, KP model), the canopy resistance r_c is parameterized by a semi‐empirical approach. In the second model (Todorovic M. 1999. Single‐layer evapotranspiration model with variable canopy resistance. Journal of Irrigation and Drainage Engineering—ASCE 125: 235–245, TD model), the resistance r_c is parameterized by a mechanistic model. These two approaches are critically analysed with respect to the underlying hypotheses and the limitations of their practical application. In the case of the KP model, the mean slope between measured and calculated values of λE was 1·01 ± 0·6 and the relative correlation coefficients r² ranged between 0·8 and 0·93. The observed differences in slopes, between 0·96 and 1·07, were not associated with the crop height. This model seemed to be applicable to all the crops examined. In the case of the TD model, the observed slope between measured and calculated values of λE for the grass canopy was 0·79. For the other crops, it varied between 1·24 and 1·34. In all the situations examined, the values of r² ranged between 0·73 and 0·92. The TD model underestimated λE in the case of grass and overestimated it in the cases of the other three crops. The under‐ or overestimation of λE in the TD model were due: (i) to some inaccuracies in the theory of this model, (ii) to not taking into account the effect of aerodynamic resistance r_a in the canopy resistance modelling. Therefore, the values of r_c were under‐ or overestimated in consequence of mismatching the crop height. The high value of air vapour pressure deficit also contributed to the overestimation of λE, mainly for the tallest crop. The results clarify aspects of the scientific controversy in the literature about the mechanistic and semi‐empirical approaches for estimating λE. From the practical point of view the results also present ways for identifying the most appropriate approach for the experimental situations encountered. Copyright © 2010 John Wiley & Sons, Ltd.     

Impact of lateral flow and spatial scaling on the simulation of semi‐arid urban land surfaces in an integrated hydrologic and land surface model

Understanding and representing hydrologic fluxes in the urban environment is challenging because of fine scale land cover heterogeneity and lack of coherent scaling relationships. Here, the impact of urban land cover heterogeneity, scale, and configuration on the hydrologic and surface energy budget (SEB) is assessed using an integrated, coupled land surface/hydrologic model at high spatial resolutions. Archetypes of urban land cover are simulated at varying resolutions using both the National Land Cover Database (NLCD; 30 m) and an ultra high‐resolution land cover dataset (0.6 m). The analysis shows that the impact of highly organized, yet heterogeneous, land cover typical of the urban domain can cause large variations in hydrologic and energy fluxes within areas of similar land cover. The lateral flow processes that occur within each simulation create variations in overland flow of up to ±200% and ±4% in evapotranspiration. The impact on the SEB is smaller and largely restricted to the wet season for our semi‐arid forcing scenarios. Finally, we find that this seasonal bias, predominantly caused by lateral flow, is displaced by a systematic diurnal bias at coarser resolutions caused by deficiencies in the method used for scaling of land surface and hydrologic parameters. As a result of this research, we have produced land surface parameters for the widely used NLCD urban land cover types. This work illustrates the impact of processes that remain unrepresented in traditional high‐resolutions land surface models and how they may affect results and uncertainty in modeling of local water resources and climate. Copyright © 2015 John Wiley & Sons, Ltd.     

Evaluation of a surface energy balance method based on optical and thermal satellite imagery to estimate root‐zone soil moisture

Various remote‐sensing methods are available to estimate soil moisture, but few address the fine spatial resolutions (e.g. 30‐m grid cells) and root‐zone depth requirements of agricultural and other similar applications. One approach that has been previously proposed to estimate fine‐resolution soil moisture is to first estimate the evaporative fraction from an energy balance that is inferred from optical and thermal remote‐sensing images [e.g. using the Remote Sensing of Evapotranspiration (ReSET) algorithm] and then estimate soil moisture through an empirical relationship to evaporative fraction. A similar approach has also been proposed to estimate the degree of saturation. The primary objective of this study is to evaluate these methods for estimating soil moisture and degree of saturation, particularly for a semi‐arid grassland with relatively dry conditions. Soil moisture was monitored at 28 field locations in south‐eastern Colorado with herbaceous vegetation during the summer months of 3 years. In situ soil moisture and degree of saturation observations are compared with estimates calculated from Landsat imagery using the ReSET algorithm. The in situ observations suggest that the empirical relationships with evaporative fraction that have been proposed in previous studies typically provide overestimates of soil moisture and degree of saturation in this region. However, calibrated functions produce estimates with an accuracy that may be adequate for various applications. The estimates produced by this approach are more reliable for degree of saturation than for soil moisture, and the method is more successful at identifying temporal variability than spatial variability in degree of saturation for this region. Copyright © 2015 John Wiley & Sons, Ltd.     

Groundwater quality in the semi‐arid region of the Chahardouly basin,West Iran

Chahardouly basin is located in the western part of Iran and is characterized by semi‐arid climatic conditions and scarcity in water resources. The main aquifer systems are developed within alluvial deposits. The availability of groundwater is rather erratic owing to the occurrence of hard rock formation and a saline zone in some parts of the area. The aquifer systems of the area show signs of depletion, which have taken place in recent years due to a decline in water levels. Groundwater samples collected from shallow and deep wells were analysed to examine the quality characteristics of groundwater. The major ion chemistry of groundwater is dominated by Ca²⁺ and HCO₃^?, while higher values of total dissolved solids (TDS) in groundwater are associated with high concentrations of all major ions. An increase in salinity is recorded in the down‐gradient part of the basin. The occurrence of saline groundwater, as witnessed by the high electrical conductivity (EC), may be attributed to the long residence time of water and the dissolution of minerals, as well as evaporation of rainfall and irrigation return flow. Based on SAR values and sodium content (%Na), salinity appears to be responsible for the poor groundwater quality, rendering most of the samples not suitable for irrigation use. Copyright © 2007 John Wiley & Sons, Ltd.     

Semi classical gravitational effects around global monopole in Kalb-Ramond background

The problem of semiclassical gravitational effects of globalmonopole in Kalb-Ramond backgroundinvestigated. It is shown that the monopoleexerts repulsive gravitational force on nonrelativistic matter and space around it hasa deficit solid angle.     

Parameter estimation in semi‐distributed hydrological catchment modelling using a multi‐criteria objective function

Output generated by hydrologic simulation models is traditionally calibrated and validated using split‐samples of observed time series of total water flow, measured at the drainage outlet of the river basin. Although this approach might yield an optimal set of model parameters, capable of reproducing the total flow, it has been observed that the flow components making up the total flow are often poorly reproduced. Previous research suggests that notwithstanding the underlying physical processes are often poorly mimicked through calibration of a set of parameters hydrologic models most of the time acceptably estimates the total flow. The objective of this study was to calibrate and validate a computer‐based hydrologic model with respect to the total and slow flow. The quick flow component used in this study was taken as the difference between the total and slow flow. Model calibrations were pursued on the basis of comparing the simulated output with the observed total and slow flow using qualitative (graphical) assessments and quantitative (statistical) indicators. The study was conducted using the Soil and Water Assessment Tool (SWAT) model and a 10‐year historical record (1986–1995) of the daily flow components of the Grote Nete River basin (Belgium). The data of the period 1986–1989 were used for model calibration and data of the period 1990–1995 for model validation. The predicted daily average total flow matched the observed values with a Nash–Sutcliff coefficient of 0·67 during calibration and 0·66 during validation. The Nash–Sutcliff coefficient for slow flow was 0·72 during calibration and 0·61 during validation. Analysis of high and low flows indicated that the model is unbiased. A sensitivity analysis revealed that for the modelling of the daily total flow, accurate estimation of all 10 calibration parameters in the SWAT model is justified, while for the slow flow processes only 4 out of the set of 10 parameters were identified as most sensitive. Copyright © 2007 John Wiley & Sons, Ltd.