High Rainfall Variability Research Articles

Rainfall risk and the potential of reduced tillage systems to conserve soil water in semi-arid cropping systems of southern Africa

Improvement of household food security in the Limpopo Basin has been elusive due to a combination of factors related to information and market constraints, but also farmers’ risk aversion induced by the high variability of rainfall during the growing season. The purpose of this study was to (1) characterize the rainfall and growing season patterns experienced by smallholder farmers, and (2) measure soil water dynamics in ripper and basin tillage systems being promoted in the semi-arid Limpopo Basin of southern Africa. The results show that the second half of the growing season receives more rainfall than the first half in the Limpopo Basin. However, rainfall is more variable during the January-March than the October-December period. Growing seasons start earlier and end later in the Mozambique part of the basin which is closer to the Indian Ocean. The Limpopo Basin is prone to two and three week dry spells with chances of 14 day spells higher (34–42%) than the 21 day spells (8–12%). The chances of 14 and 21 day dry spells increase substantially during the second half of the growing season. The 1980–1990 was one of the driest decades in the Limpopo Basin. Planting basin system conserved more soil water on sandy loam (18–24%) and clay loam (4–12%) soils than the conventional practice during flowering and grain filling maize growth stages. Ripper had 17–29% more soil water than conventional practice during flowering and grain filling maize growth stages. There is a high risk of dry spells and soil water deficits in smallholder cropping systems of the Limpopo basin. There is therefore scope in promoting rain and soil water management technologies, and good land husbandry in order to reduce risk of crop failure in the smallholder cropping systems.

Identification of Drought Prone Areas and Trend Analysis of Rainfall Phenomenon in Dhasan Basin

The present study has been focussed to recognize and quantify the drought condition in Dhasan basin which falls in drought prone region of Bundelkhand (Madhya Pradesh). The area is under frequent occurrence of droughts since decades due to irregularity in arrival of rainfall. The high variability of the annual rainfall is one of the primary causes of the drought prevailing in the Dhasan basin on a regular basis. The decreasing trend of rainfall may further aid to drought severity. The rainfall departure analysis indicated that, the study area is under the grip of regular and continuous droughts with the drought frequency varying between once in 2 years to once in 3 years, which is rather very high. Sagar and Banda areas were identified to be most drought prone followed by Khurai.

Variability Space-Temporal of Annual Precipitation of Wet and Dry Period in the Paraíba State

Rainfall is considered an important climatological variable in the semiarid region of Brazil, mainly due to irregularity in its temporal and spatial distribution. It has been aimed at achieving the analysis of spatio-temporal variability of rainfall, maximum, minimum and average annual for the State of Paraíba. Data were used with 30 or more years of observation, analysis was carried out for consistency and homogeneity. To analyze the spatial distribution was used Surfer and their statistical software using the Kriging interpolation method which is considered a good data interpolation methodology and producing maps. From the results it is observed that in January were the most significant rainfall and isolated regions of the Sertão and Alto Sertão Paraiba. In February the distribution already became homogeneous. The months of March and April are the rainy months in every state and from May to Augusts the highest rainfall concentrated in the eastern and southern coastal strip. September considered the driest month and throughout the year rainfall occurred in isolation. The annual distribution showed high spatial variability of rainfall in the central sector of the state with minor fluctuations ranging from 300 to 500mm, in the Sertão and Alto Sertão flowed from 700 to 900mm; in Brejo and Agreste from 700 to 1,200 mm; and Litoral of 1,200 to 1,600mm

Comparing fixed and flexible stocking as adaptations to inter-annual rainfall variability in the extensive beef industry of northern Australia

Many beef producers within the extensive cattle industry of northern Australia attempt to maintain a constant herd size from year-to-year (fixed stocking), whereas others adjust stock numbers to varying degrees annually in response to changes in forage supply. The effects of these strategies on pasture condition and cattle productivity cannot easily be assessed by grazing trials. Simulation studies, which include feedbacks of changes to pasture condition on cattle liveweight gain, can extend the results of grazing trials both spatially and temporally. They can compare a large number of strategies, over long periods of time, for a range of climate periods, at locations which differ markedly in climate. This simulation study compared the pasture condition and cattle productivity achieved by fixed stocking at the long-term carrying capacity with that of 55 flexible stocking strategies at 28 locations across Queensland and the Northern Territory. Flexible stocking strategies differed markedly in the degree they increased or decreased cattle stocking rates after good and poor pasture growing seasons, respectively. The 28 locations covered the full range in average annual rainfall and inter-annual rainfall variability experienced across northern Australia. Constrained flexibility, which limited increases in stocking rates after good growing seasons to 10% but decreased them by up to 20% after poor growing seasons, provides sustainable productivity gains for cattle producers in northern Australia. This strategy can improve pasture condition and increase cattle productivity relative to fixed stocking at the long-term carrying capacity, and its capacity to do this was greatest in the semiarid rangeland regions that contain the majority of beef cattle in northern Australia. More flexible stocking strategies, which also increased stocking rates after good growing seasons by only half as much as they decreased them after poor growing seasons, were equally sustainable and more productive than constrained flexibility, but are often impractical at property and industry scales. Strategies with the highest limits (e.g. 70%) for both annual increases and decreases in stocking rates could achieve higher cattle productivity, but this was at the expense of pasture condition and was not sustainable. Constrained flexible stocking, with a 10% limit for increases and a 20% limit for decreases in stocking rates annually, is a risk-averse adaptation to high and unpredictable rainfall variability for the extensive beef industry of northern Australia.

Variable ecological conditions promote male helping by changing banded mongoose group composition

Ecological conditions are expected to have an important influence on individuals' investment in cooperative care. However, the nature of their effects is unclear: both favorable and unfavorable conditions have been found to promote helping behavior. Recent studies provide a possible explanation for these conflicting results by suggesting that increased ecological variability, rather than changes in mean conditions, promote cooperative care. However, no study has tested whether increased ecological variability promotes individual-level helping behavior or the mechanisms involved. We test this hypothesis in a long-term study population of the cooperatively breeding banded mongoose, Mungos mungo, using 14 years of behavioral and meteorological data to explore how the mean and variability of ecological conditions influence individual behavior, body condition, and survival. Female body condition was more sensitive to changes in rainfall leading to poorer female survival and pronounced male-biased group compositions after periods of high rainfall variability. After such periods, older males invested more in helping behavior, potentially because they had fewer mating opportunities. These results provide the first empirical evidence for increased individual helping effort in more variable ecological conditions and suggest this arises because of individual differences in the effect of ecological conditions on body condition and survival, and the knock-on effect on social group composition. Individual differences in sensitivity to environmental variability, and the impacts this has on the internal structure and composition of animal groups, can exert a strong influence on the evolution and maintenance of social behaviors, such as cooperative care.

Neighbour effects on shrub seedling establishment override climate change impacts in a Mediterranean community

AbstractQuestionsCan theory about plant–plant interactions along climate gradients help us predict how climate change will affect shrub establishment? How does a predicted reduction in rainfall affect the outcome of the interactions between shrub seedlings and herbaceous plants in a dryland ecosystem?LocationThree field sites along a rainfall gradient and an adjacent experimental site at the Botanical Gardens of Tel Aviv University, Israel.MethodWe measured seedling survival of a dominant shrub species in response to the presence of herbaceous neighbours and to rainfall amount using two approaches: First, we employed a space‐for‐time approach and studied seedling survival along an aridity gradient that was shown to mimic the predicted rainfall changes. Second, we monitored seedling survival in a common garden experiment in which we simulated drought using rainout shelters. In both experiments we contrasted the importance of water availability relative to the presence of herbaceous neighbours and the origin of the shrub seedlings.ResultsOur results showed that neighbours always had a negative effect on shrub seedling survival. In contrast to theoretical predictions, the intensity of competition increased with reduction in water availability. Shrub seedlings originating from drier conditions showed higher survival than seedlings from mesic origin.ConclusionsThese results emphasize the importance of incorporating biotic interactions in studies predicting changes in plant dynamics under climate change. Moreover, plant species growing in ecosystems prone to high rainfall variability showed a greater ability to cope with dry conditions, which suggests more nuanced origin‐specific predictions than suggested by recent climate models.

Strategies to improve water productivity in small tank system: a case study from Kurunegala district in Sri Lanka

The number of presently operating small tanks in the Kurunegala district is 4,482 of which 2873 tanks have less than 6 ha of command area. Capacity of these tanks is low and the amount of water stored is not sufficient to fulfil the water requirement of the rice crop throughout the cropping season. Many farmers in Udakadawala area in the Kurunegala district adopts to start land preparation (LP) after filling tanks and start LP using tank water. This situation results in the delaying of the cultivation and limiting the use of rain water during the initial stages of the crop. On the other hand, due to high variability of rainfall, severe crop damages are frequently experienced. The objectives of this study were to identify the factors affecting low water productivity and to introduce and evaluate a new land and water management approach to increase rice yields. A trans-disciplinary esearch methodology was used employing participatory research tools. Seedling broadcasting (parachute) method with proper LP technology, time of cultivation, water management practices and use of good quality seed paddy were applied to five separate plots in the field while other fields were under their normal activities. Yield components data were collected and were analyzed. According to the results obtained, farmers delayed LP until water issue from the tank and cultivation is mainly done by rotavators mounted to two wheel tractors. In treatment, early LP with onset of rainfall using four wheel tractors save water up to 66% of the total water requirement. LP using tine tiller compared to rotavator reduces the amount of water required for the LP and increase the access to more water and nutrients by increasing the root depth. Tank water productivity was 1.93 and 0.28 kg/m 3 in treatment and control, respectively. The effect is more useful in Yala than in the Maha season. “Parachute” method and other agronomic practices such as recommended seeds, using organic matter, proper weeding is important along with land and water management. Conjunctive use of rainfall and tank water in combination with other management techniques was successful in increasing water productivity in small tank irrigation system. Tropical Agricultural Research Vol. 26 (4): 684 – 692 (2015)

Understanding runoff processes in a semi-arid environment through isotope and hydrochemical hydrograph separations

Abstract. The understanding of runoff generation mechanisms is crucial for the sustainable management of river basins such as the allocation of water resources or the prediction of floods and droughts. However, identifying the mechanisms of runoff generation has been a challenging task, even more so in arid and semi-arid areas where high rainfall and streamflow variability, high evaporation rates, and deep groundwater reservoirs may increase the complexity of hydrological process dynamics. Isotope and hydrochemical tracers have proven to be useful in identifying runoff components and their characteristics. Moreover, although widely used in humid temperate regions, isotope hydrograph separations have not been studied in detail in arid and semi-arid areas. Thus the purpose of this study is to determine whether isotope hydrograph separations are suitable for the quantification and characterization of runoff components in a semi-arid catchment considering the hydrological complexities of these regions. Through a hydrochemical characterization of the surface water and groundwater sources of the catchment and two- and three-component hydrograph separations, runoff components of the Kaap catchment in South Africa were quantified using both isotope and hydrochemical tracers. No major disadvantages while using isotope tracers over hydrochemical tracers were found. Hydrograph separation results showed that runoff in the Kaap catchment is mainly generated by groundwater sources. Two-component hydrograph separations revealed groundwater contributions of between 64 and 98 % of total runoff. By means of three-component hydrograph separations, runoff components were further separated into direct runoff, shallow and deep groundwater components. Direct runoff, defined as the direct precipitation on the stream channel and overland flow, contributed up to 41 % of total runoff during wet catchment conditions. Shallow groundwater defined as the soil water and near-surface water component (and potentially surface runoff) contributed up to 45 % of total runoff, and deep groundwater contributed up to 84 % of total runoff. A strong correlation for the four studied events was found between the antecedent precipitation conditions and direct runoff. These findings suggest that direct runoff is enhanced by wetter conditions in the catchment that trigger saturation excess overland flow as observed in the hydrograph separations.

Maize root development and grain production as affected by soil and water management on a sandy soil in a semi-arid region of southern Mozambique

ABSTRACTAverage yield of maize (Zea mays L.) in Mozambique is low, mainly due to low use of inputs in agriculture, high seasonal rainfall variability and inadequate soil preparation. A study conducted in two summer crop seasons (November–March 2012/2013 and 2013/2014) examined the impact of three tillage methods (hand hoeing, strip tillage and conventional tillage), two fertiliser levels (0 and 40% N) and two water supply regimes (rainfed and irrigated) on maize root development and grain yield on a sandy soil in a semi-arid region of Mozambique. Tillage had a major effect on soil penetration resistance, but little effect on root growth and limited effect on yield. Thus, there appears to be little need for loosening on this soil. There was also no interaction between tillage and the other experimental factors, meaning that tillage system can be chosen irrespective of fertiliser and water supply. Irrigation had the largest impact on root and shoot growth and crop yield, increasing yield in season 2 from 670 to 4780 kg ha–1.There was a very strong interaction between fertiliser and water supply, with no yield increase for fertiliser in the rainfed treatment, while combined with irrigation it increased yield by 1590 kg ha–1 in season 1 and 1840 kg ha–1 in season 2. Thus, for the conditions studied here, it was rational to add fertiliser only in combination with irrigation and not in a rainfed system.

English

Barley (Hordeum vulgare L.) is a major food crop in Ethiopia. A high inter-annual rainfall variability, concomitant variable planting dates and unpredictable drought stress at any time during the rainy season are severe constraints to barley production in Ethiopia. To study genotype by environment (G x E) interactions and grain yield stability, 18 barley genotypes (three landraces and 15 improved cultivars) were evaluated for yield and flowering time in two locations (Ambo and Jimma) and four staggered sowing dates over two years (2012-2013) giving a total of 16 environments. It was observed a wide phenotypic variation over environments for both grain yield (677-2,944 kg ha-1) and days to 50% flowering (63-82 days). Considering the 18 genotypes and 16 environments, both genotype (G) and G x E interaction variance components were highly significant for grain yield, with a ratio of approximately 1:1. The G x E analysis revealed that the first two interaction principal component axes (IPCA1 and IPC2) in an additive main effect and multiplicative interaction (AMMI) model explained 66.1% of the total G x E interaction for grain yield (P < 0.001). Of the 16 environments, 12 grouped into two clusters which largely corresponded to test locations. The tested genotypes revealed a wide variation for both static and dynamic yield stability measures. Compared to improved cultivars, farmers' landraces displayed higher average static stability (e.g. IPCA1; P = 0.017) and similar superiority indices (dynamic stability). These landraces are therefore a source of germplasm for breeding resilient barley cultivars. Staggered planting proved to be a useful method for evaluating genotype stability across environmental factors beyond location and season. Key words: G x E interaction, additive main effect and multiplicative interaction (AMMI), stability, landrace, barley, Ethiopia.

Development and assessment of non-linear and non-stationary seasonal rainfall forecast models for the Sirba watershed, West Africa

Abstract Study region The Sirba watershed, Niger and Burkina Faso countries, West Africa. Study focus Water resources management in the Sahel region, West Africa, is extremely difficult because of high inter-annual rainfall variability. Unexpected floods and droughts often lead to severe humanitarian crises. Seasonal rainfall forecasting is one possible way to increase resilience to climate variability by providing information in advance about the amount of rainfall expected in each upcoming rainy season. Rainfall forecasting models often arbitrarily assume that rainfall is linked to predictors by a multiple linear regression with parameters that are independent of time and of predictor magnitude. Two probabilistic methods based on change point detection that allow the relationship to change according to time or rainfall magnitude were developed in this paper using normalized Bayes factors. Each method uses one of the following predictors: sea level pressure, air temperature and relative humidity. Method M1 allows for change in model parameters according to annual rainfall magnitude, while M2 allows for changes in model parameters with time. M1 and M2 were compared to the classical linear model with constant parameters (M3) and to the climatology (M4). New hydrological insights for the region The model that allows a change in the predictor–predictand relationship according to rainfall amplitude (M1) and uses air temperature as predictor is the best model for seasonal rainfall forecasting in the study area.

SEQUENTIAL EFFECTS OF MINIMUM TILLAGE, SEED PRIMING, FERTILIZER MICRODOSING AND MULCHING IN MAIZE, SEMIARID CENTRAL RIFT VALLEY OF ETHIOPIA

SUMMARYIntensification of maize production is imperative to improve food security for the rising population in the central rift valley (CRV) of Ethiopia, whose livelihood is principally based on rainfed maize that operates under shrinking landholding and high seasonal rainfall variability. This study examined different levels of intensification options in maize production by sequentially introducing minimum tillage and seed priming, phosphorus (P) fertilizer microdosing, surface mulching and nitrogen (N) fertilizer microdosing. Field experiments were conducted with five treatments, steps or levels consisting of conventional tillage (farmers practice as a control); minimum tillage + seed priming, unfertilized (step 1); step 1 + microdosing 53 kg ha−1 P (step 2); step 2 + 4 ton ha−1 maize stover as surface mulch (step 3) and step 3 + 53 kg ha−1 N (step 4). These steps represented increasing levels of intensification. Except at the lowest level (step 1), agronomic and economic responses improved with increasing levels of inputs. Relative to the very high and increasing gross margin, production costs were low but slowly increased with increasing levels of inputs. Except at the lowest level, the value cost ratio was above 4 even at the highest levels of inputs, demonstrating that such kind of intensification can be achieved with low risk. Likewise, the fertilizer use efficiency was quite high even at the highest of levels of inputs signifying the efficiency of the pocket application of fertilizer through the microdosing method. The improvement in maize establishment and yield and the reduction in the days to maturity could contribute to make maize production more adaptive to the existing seasonal rainfall variability. Depending on the affordability to the external inputs and their feasibilities, the different technology packages in the intensification ladder may give different choices for the farmers to improve maize production in the CRV of Ethiopia.

Vulnerability of Tea Sector for Climate Change in the Major Tea Growing Regions in Central Hills of Sri Lanka

The climate change impacts are becoming a prominent issue in the Sri Lankan tea sector. This study has attempted to identify vulnerability of tea sector in the major tea growing district of Nuwara Eliya in the central hills of Sri Lanka. Mean monthly rainfall and temperature, drought conditions and soil erosion of Nuwara Eliya district were considered as major variables in climate vulnerability mapping. Climate vulnerability map was developed using weighted overlay modeling in Geographic Information Systems (GIS) by allocating appropriate weightages for the main variables mentioned above for their influence on tea production. Rainfall data analysis for the study period from 1945 to 2005 revealed significantly higher rainfall variability for months of January, June, July, and August, which highlights the need of special management attention in these months. Around 65% of land extent of the study area possessed an ideal temperature regime (18-250C) for growth of tea. Land extent of 3.96% under tea was highly vulnerable for soil erosion in the study area. Less and moderately soil erosion vulnerable tea extent were 79.64% and 16.40%, respectively. The climate vulnerability map developed based on all four variables, revealed that 13.15% tea extent as highly vulnerable for current climate change. Land extent of 20.54% and 66.31% were categorized as moderately and less climate vulnerable, respectively, which could also become vulnerable in future, if present trends continues. Necessary adaptation strategies should therefore be implemented immediately to ensure the sustainability of the tea industry in the central hill region of Sri Lanka. Journal of Environmental Professionals Sri Lanka: 2015 Vol. 4 No. 1: 29-48

Impacts of high inter-annual variability of rainfall on a century of extreme hydrologic regime of northwest Australia

Abstract. Long-term hydrologic records provide crucial reference baselines of natural variability that can be used to evaluate potential changes in hydrologic regimes and their impacts. However, there is a dearth of studies of the hydrologic regimes for tropical drylands where intraseasonal and interannual variability in magnitude and frequency of precipitation are extreme. Here, we sought to identify the main hydroclimatic determinants of the strongly episodic flood regime of a large catchment in the semi-arid, subtropical northwest of Australia and to establish the background of hydrologic variability for the region over the last century. We used a monthly sequence of satellite images to quantify surface water expression on the Fortescue Marsh, the largest water feature of inland northwest Australia, from 1988 to 2012. We used this sequence together with instrumental rainfall data to build a statistical model with multiple linear regression and reconstruct monthly history of floods and droughts since 1912. We found that severe and intense regional rainfall events, as well as the sequence of recharge events both within and between years, determine surface water expression on the floodplain (i.e. total rainfall, number of rain days and carried-over inundated area; R2adj = 0.79; p value &lt; 0.001, ERMSP = 56 km2). The most severe reconstructed inundation over the last century was in March 2000 (1000 km2), which is less than the 1300 km2 area required to overflow to the adjacent catchment. The Fortescue Marsh was completely dry for 32% of all years, for periods of up to four consecutive years. Extremely wet years (seven of the 100 years) caused the Marsh to remain inundated for up to 12 months; only 25% of years (9% of all months) had floods of greater than 300 km2. The prolonged, severe and consecutive yearly inundations between 1999 and 2006 were unprecedented compared to the last century. While there is high inter-annual variability in the system, if the frequency and intensity of extreme rainfall events for the region were to increase (or be similar to 1999–2006), surface water on the Marsh will become more persistent, in turn impacting its structure and functioning as a wetland.

Hydrological assessment of TRMM rainfall data over Yangtze River Basin

High-quality rainfall information is critical for accurate simulation of runoff and water cycle processes on the land surface. In situ monitoring of rainfall has a very limited utility at the regional and global scale because of the high temporal and spatial variability of rainfall. As a step toward overcoming this problem, microwave remote sensing observations can be used to retrieve the temporal and spatial rainfall coverage because of their global availability and frequency of measurement. This paper addresses the question of whether remote sensing rainfall estimates over a catchment can be used for water balance computations in the distributed hydrological model. The TRMM 3B42V6 rainfall product was introduced into the hydrological cycle simulation of the Yangtze River Basin in South China. A tool was developed to interpolate the rain gauge observations at the same temporal and spatial resolution as the TRMM data and then evaluate the precision of TRMM 3B42V6 data from 1998 to 2006. It shows that the TRMM 3B42V6 rainfall product was reliable and had good precision in application to the Yangtze River Basin. The TRMM 3B42V6 data slightly overestimated rainfall during the wet season and underestimated rainfall during the dry season in the Yangtze River Basin. Results suggest that the TRMM 3B42V6 rainfall product can be used as an alternative data source for large-scale distributed hydrological models.

English

This study was conducted to investigate historical climate dynamics and the resultant risks at four sites (Meki, Melkassa, Miesso and Ziway) in the Central Rift Valley of Ethiopia. It involved analysis of rainfall and temperature data in the study areas. The results showed the existence of high inter-annual rainfall variability within seasons and sites. The number of rainy days exhibited a declining trend at Meki in both belg (FMAM) and kiremt (JJAS) seasons and an increasing trend at Melkassa in the belg season; while an increasing trend was observed at Miesso and Ziway in the kiremt season, and no change in trends was observed in the belg season at both sites. The minimum and maximum temperature showed an increasing trend at Miesso and Ziway, whereas no change was observed at Melkassa. As opposed to the cessation of the rainfall, onset dates of rainfall were highly variable at all sites. The median length of the growing period was found to be 101, 88, 118 and 104 days at Meki, Melkassa, Miesso and Ziway, respectively. The obtained results will certainly help the farming community and the agricultural sector to make a decision for the best management scheme in the central rift valley of Ethiopia. Key words: Climate change, risk, rainfall, temperature, crop production, Central Rift Valley, Belg, Kiremt.

Zonal winds and southeast Australian rainfall in global and regional climate models

Southeast Australia is a region of high rainfall variability related to major climate drivers, with a long-term declining trend in cool-season rainfall. Projections of future rainfall trends are uncertain in this region, despite projected southward shifts in the subtropical ridge and mid-latitude westerlies. This appears to be related to a poor representation of the spatial relationships between rainfall variability and zonal wind patterns across southeast Australia in the latest Coupled Model Intercomparison Project ensemble, particularly in the areas where weather systems embedded in the mid-latitude westerlies are the main source of cool-season rainfall. Downscaling with regional climate models offers improvements in the mean rainfall climatology, and shows some ability to correct for poor modelled relationships between rainfall and zonal winds along the east coast of Australia. However, it provides only minor improvements to these relationships in southeast Australia, despite the improved representation of topographic features. These results suggest that both global and regional climate models may fail to translate projected circulation changes into their likely rainfall impacts in southeast Australia.

Governance and management of local water storage in the Hindu Kush Himalayas

The people of the Hindu Kush Himalayan region face severe seasonal water shortages due to the high variability in rainfall, and the problem is likely to be exacerbated under climate change. Small-scale local water storage options offer a means of collecting monsoon precipitation to provide for agricultural and household needs over the entire year, and they help build community resilience. Proper watershed management, with due consideration of upstream–downstream linkages, and appropriate institutional arrangements are vital for this adaptation measure to work. Active participation of local users in decisions related to water allocation and community services is essential. Planned interventions should preserve the institutional arrangements of reciprocity and cooperation among community members.

Climate variability and water resource scarcity in drylands of Rajasthan, India

The world is experiencing a high climatic variability and has its impact on all ecosystems, regions and sectors, but the nature and extent of vulnerability to climate change differs with adaptive capacity of individual, society and region. The regions which are scarce on resources are among the very vulnerable systems of the earth and most of such regions have existing extreme climatic conditions like deserts and snow covered areas. The vulnerability of arid regions is further accentuated by low levels of socio-economic development, and this is the case with arid regions of India, which leads to fast depletion of water resources. The study analyses the climate variability over last 35 years (1973–2008) in the Western drylands of Rajasthan and the results show that the temperature has shown a great variability with an average rise of about 0.5°C for the month of June. The maximum rise is visible during 1995–2000. The scarcity of water resource accompanied by variability creates water stress conditions in the region and is responsible for droughts. During last 35 years (1973–2008) the average annual rainfall has shown a decrease of 50 mm. With an overall rise in temperature over the region and changing precipitation trends the humidity provinces as defined by Thornthwaite have shifted eastward. The climate variability has direct impact on the water resources of the region. The low to medium rainfall in most parts, high evapo-transpiration demands for water, high frequency of occurrence of droughts resulting from the departure of rainfall from mean values, and the high per capita arable land increases the demand for irrigation water. The free power in agriculture continued for many years, and the existing pump horse power based pricing of electricity encourage over-pumping and inefficient and often wasteful use of groundwater. The advent of Indira Gandhi Canal in the fragile desert ecosystems helps the region to cope with high variability in rainfall. The study suggests that water security in the region can be attained through expansion of canal network.

Potential of deterministic and geostatistical rainfall interpolation under high rainfall variability and dry spells: case of Kenya’s Central Highlands

Drier parts of Kenya’s Central Highlands endure persistent crop failure and declining agricultural productivity. These have, in part, attributed to high temperatures, prolonged dry spells and erratic rainfall. Understanding spatial-temporal variability of climatic indices such as rainfall at seasonal level is critical for optimal rain-fed agricultural productivity and natural resource management in the study area. However, the predominant setbacks in analysing hydro-meteorological events are occasioned by either lack, inadequate, or inconsistent meteorological data. Like in most other places, the sole sources of climatic data in the study region are scarce and only limited to single stations, yet with persistent missing/unrecorded data making their utilization a challenge. This study examined seasonal anomalies and variability in rainfall, drought occurrence and the efficacy of interpolation techniques in the drier regions of eastern Kenyan. Rainfall data from five stations (Machang’a, Kiritiri, Kiambere and Kindaruma and Embu) were sourced from both the Kenya Meteorology Department and on-site primary recording. Owing to some experimental work ongoing, automated recording for primary dailies in Machang’a have been ongoing since the year 2000 to date; thus, Machang’a was treated as reference (for period of record) station for selection of other stations in the region. The other stations had data sets of over 15 years with missing data of less than 10 % as required by the world meteorological organization whose quality check is subject to the Centre for Climate Systems Modeling (C2SM) through MeteoSwiss and EMPA bodies. The dailies were also subjected to homogeneity testing to evaluate whether they came from the same population. Rainfall anomaly index, coefficients of variance and probability were utilized in the analyses of rainfall variability. Spline, kriging and inverse distance weighting interpolation techniques were assessed using daily rainfall data and digital elevation model in ArcGIS environment. Validation of the selected interpolation methods were based on goodness of fit between gauged (observed) and generated rainfall derived from residual errors statistics, coefficient of determination (R 2), mean absolute errors (MAE) and root mean square error (RMSE) statistics. Analyses showed 90 % chance of below cropping-threshold rainfall (500 mm) exceeding 258.1 mm during short rains in Embu for 1 year return period. Rainfall variability was found to be high in seasonal amounts (e.g. coefficient of variation (CV) = 0.56, 0.47, 0.59) and in number of rainy days (e.g. CV = 0.88, 0.53) in Machang’a and Kiritiri, respectively. Monthly rainfall variability was found to be equally high during April and November (e.g. CV = 0.48, 0.49 and 0.76) with high probabilities (0.67) of droughts exceeding 15 days in Machang’a. Dry spell probabilities within growing months were high, e.g. 81 and 60 % in Machang’a and Embu, respectively. Kriging interpolation method emerged as the most appropriate geostatistical interpolation technique suitable for spatial rainfall maps generation for the study region.