Dry Sub-humid Regions Research Articles

Characterization of Soil Particle Size Distribution with a Fractal Model in the Desertified Regions of Northern China

We constructed an aeolian soil database across arid, semi-arid, and dry sub-humid regions, China. Soil particle size distribution was measured with a laser diffraction technique, and fractal dimensions were calculated. The results showed that: (i) the predominant soil particle size distributed in fine and medium sand classifications, and fractal dimensions covered a wide range from 2.0810 to 2.6351; (ii) through logarithmic transformations, fractal dimensions were significantly positive correlated with clay and silt contents (R2 = 0.81 and 0.59, P < 0.01), and significantly negative correlated with sand content (R2 = 0.50, P < 0.01); (3) hierarchical cluster analysis divided the plots into three types which were similar to sand dune types indicating desertification degree. In a large spatial scale, fractal dimensions are still sensitive to wind-induced desertification. Therefore, we highly recommend that fractal dimension be used as a reliable and quantitative parameter to monitor soil environment changes in desertified regions. This improved information provides a firm basis for better understanding of desertification processes.

Comparative study of reference evapotranspiration estimation methods including Artificial Neural Network for dry sub-humid agro-ecological region

In the present study, an attempt has been made to compare the reference evapotranspiration (ETo), computed by eight different methods, namely, Penman-Monteith, Modified Penman-Monteith, Hargreaves-Samani, Irmak, Hargreaves, Valiantzas, ANN and FAO(24) model for the dry subhumid agro-ecological region (Varanasi). An attempt was also made to find out utility of artificial neural networks (ANN) for estimation of ET0 with minimum input. Feed forward network has been used for prediction of ETo using resilient back-propagation method and the architecture 2–21(having parameters Tmean and solar radiation) was found to be the best one. The average annual evapotranspiration (by Penman-Monteith method) for Varanasi was found to be 1447.4 mm. When compared among the different methods for estimation of reference evapotranspiration with Penman-Monteith method, the FAO-24 and Hargraves-Samani (3) under estimate, however, Modified Penman-Monteith, Hargreaves-Samani, Irmak, Hargreaves, Valiantzas over-estimate and ANN closely estimates reference evapotranspiration.

Comparison of dryland climate change in observations and CMIP5 simulations

A comparison of observations with 20 climate model simulations from the Coupled Model Intercomparison Project, Phase 5 (CMIP5) revealed that observed dryland expansion amounted to 2.61×106 km2 during the 58 years from 1948 to 2005, which was four times higher than that in the simulations (0.55×106 km2). Dryland expansion was accompanied by a decline in aridity index (AI) (drying trend) as a result of decreased precipitation and increased potential evapotranspiration across all dryland subtype areas in the observations, especially in the semi-arid and dry subhumid regions. However, the CMIP5 multi-model ensemble (MME) average performed poorly with regard to the decreasing trends of AI and precipitation. By analyzing the factors controlling AI, we found that the overall bias of AI in the simulations, compared with observations, was largely due to limitations in the simulation of precipitation. The simulated precipitation over global drylands was substantially overestimated compared with observations across all subtype areas, and the spatial distribution of precipitation in the MME was largely inconsistent in the African Sahel, East Asia, and eastern Australia, where the semi-arid and dry subhumid regions were mainly located.

Causes and Impacts of Land Degradation and Desertification: Case Study of the Sudan

Desertification, a phenomenon referring to land degradation in arid, semi-arid and dry sub-humid regions as a result of climatic variations and human activities, is considered as one of the most severe environmental and socio-economic problems o f recent times. The p rincipal aim o f th is study was to exp lore the impacts of desertification, degradation and drought on both the natural resources and man's livelihood in the Sudan and to suggest appropriate forest resource management interventions. The study was based on a fact finding tour in the Sudan and data collection on drought trends as reflected in rainfall trends in the study area, and on trends concerning the productivity of natural resources. Information was also comp iled fro m existing records on rainfall, forest land cover, forest stocking, rangelands and carrying capacity and on agricultural p roductivity and population trends. Results showed that in rain-fed agricultural zones in the Sudan, deep ploughing and leveling of the surface soil caused an increase in its susceptibility to wind erosion, wh ich, in turn, has led to a severe decline in its fertility and, in some places, the formation of sand dunes. The implications of these trends on the natural resource base include environmental degradation, food insecurity and aggravation of inco me inequalit ies among the Sudanese producers. The study has suggested Agroforestry technology as a potential solution to this continued problem of declining ru ral ag ricu ltural production in the Sudan.

Dryland expansion in northern China from 1948 to 2008

This study examines the expansion of drylands and regional climate change in northern China by analyzing the variations in aridity index (AI), surface air temperature (SAT), precipitation and potential evapotranspiration (PET) from 1948 to 2008. It is found that the drylands of northern China have expanded remarkably in the last 61 years. The area of drylands of the last 15 years (1994–2008) is 0.65×106 km2 (12%) larger than that in the period 1948–62. The boundary of drylands has extended eastward over Northeast China by about 2° of longitude and by about 1° of latitude to the south along the middle-to-lower reaches of the Yellow River. A zonal band of expansion of semi-arid regions has occurred, stretching from western Heilongjiang Province to southern Gansu Province, while shifts to the east of semi-arid regions in dry subhumid regions have also occurred. Results show that the aridity trend of drylands in northern China is highly correlated with the long-term trend of precipitation and PET, and the expansion of semi-arid regions plays a dominant role in the areal extent of drylands, which is nearly 10 times larger than that in arid and subhumid regions.

Assessing Agricultural Vulnerability in India using NDVI Data Products

Abstract. Impact of climate change on Indian rainfed agriculture was assessed using temporal NDVI data products from AVHRR and MODIS. Agricultural vulnerability was analysed using CV of Max NDVI from NOAA-AVHRR (15-day, 8 km) and MODIS-TERRA (16-day, 250 m) NDVI data products from 1982–2012. AVHRR dataset was found suitable for estimating regional vulnerability at state and agro-eco-sub-region (AESR) level while MODIS dataset was suitable for drawing district-level strategy for adaptation and mitigation. Methodology was developed to analyse NDVI variations with spatial pattern of rainfall using 10 X 10 girded data and spatially interpolating it to estimate Standard Precipitation Index. Study indicated large variations in vegetation dynamics across India owing to bio-climate and natural resource base. IPCC framework of vulnerability and exposure was used to identify vulnerable region extending from arid western India to semi-arid and dry sub-humid regions in central India and southern peninsula. This is a major agricultural region in the country with sizable human and livestock population with millions of marginal and small farm holdings. Exposure to climatic variability at local and regional levels have national implications and study indicated that over 122 districts extending over 110 mha was vulnerable to climate change that spread across 26 typical AESR in 11 states in India. Of the 74 mha under agriculture in the region, MODIS dataset indicated 47 mha as agriculturally vulnerable while coarser resolution of AVHRR dataset indicated a conservative estimate of 29 mha. First ever estimates of agricultural vulnerability for India indicates 20.4 to 33.1 % agricultural land under risk from climate change.

Dynamic and dry/wet variation of climate in the potential extent of desertification in China during 1981–2010

The potential extent of desertification in China (PEDC), composed by arid, semi-arid and dry sub-humid regions, was re-determined using a high spatial resolution meteorological dataset (1981–2010) and by applying the Thornthwaite method, which was recommended by the UNCCD for division of dryland zones (extremely arid, arid, semi-arid, dry sub-humid zones). The dynamic and the dry/wet trends in climatic variation in the general PEDC during 1981–2010 were statistically analyzed using several different methods. The newly calculated area of the general PEDC is approximately 3.222 × 106 km2, accounting for 33.6 % of China’s terrestrial. However, the results of a decadal spatial analysis indicated that the actual reduction appeared in the western region, where the general PEDC shrank to lower altitude areas. Meanwhile, the eastern border of the general PEDC was expanded to the east and southeast. Over three decades, the lower mountainous areas in northwestern Qinghai-Tibetan Plateau have experienced an obviously alternating process of drought–wetness–drought, the semi-arid and dry sub-humid regions in the east of the Helan Mountains as well as the Junggar Basin have experienced an alternating process of wetness–drought–wetness, and the vast arid region in the west of the Helan Mountains has experienced a process of drought–drought–wetness. In the most recent decade, most areas, except for the major western mountainous regions, have been experiencing a wet trend, which is favorable for combating desertification.

Hazard Assessment of Desertification as a Result of Soil and Water Recourse Degradation in Kashan Region, Iran

Desertification in arid, semi-arid and dry sub-humid regions is a global environmental problem. Considering theincreasing importance of desertification and its complexity, the necessity of giving attention to desertification criteria andindices is essential. Models and methods such as MEDALUS, UNEP-FAO, and others have been proposed on local andnational scales. In this research, IMDPA was selected from among different existing methods, and desertification intensitywas evaluated on the basis of two criteria, soil and water, and 13 indices: soil depth, electrical conductivity of soil, texture,gravel percentage, drainage, sodium absorption ratio, type of geologic formation, slope, groundwater table fluctuation,electrical conductivity of water, color concentration, water crisis index, and water shortage for livestock and wildlife.Each criterion was assessed based on the selected indices which resulted in the qualitative mapping of each criterion basedon the geometric average of the indices. Finally, a sensitive map of the region was extracted using the geometric averageof all criteria. Thematic databases with a 1:50000 scale resolution were integrated and elaborated in a GIS based onILWIS and arcGIS. Analysis of desertification criteria in the Kashan region showed that, among the studied criteria, watercriterion is a major problem in the study area. It has a geometric average of 3.59 which shows very high class, while soilcriterion with a weighted average of 2.12 stands in the medium class of desertification. The results also showed thatgroundwater decrease and water crisis index with a quantitative value of 3.72 classified in a very high class of degradationand depth with quantitative value of 1.20 classified in a low class of desertification were the most and least effectivefactors, respectively, among the studied indices on land degradation.

Integrating lucerne (Medicago sativa L.) into a high country merino system

Abstract Farm systems in the dry sub-humid region of the Upper Waitaki predominantly graze merino ewes on extensive oversown and topdressed hill and high country. Smaller areas of flatter land are used to conserve winter forage crops, and grow supplementary feed and high quality pastures. The slow growth rate of merino lambs means they are traditionally retained on these improved pastures to finish in the following spring. In this system livestock demand peaks in the driest month of January and continues to be high through winter. Bog Roy is a farm that has changed this system and has established 200 ha of lucerne with the goal of fully feeding ewes during lactation. Pre-weaning lamb growth rate has increased from 205 to 235 g/head/day, opening the opportunity to sell heavier lambs in early January. Ewe lamb replacements are reaching heavier pre-winter live weights (38 kg versus 35 kg) and the flow-on effect is higher two-tooth scanning (129% versus 111%) and weaning (100% versus 84%). Lucerne has also improved the feeding of mixed age ewes from lambing to weaning, and lamb mortality has reduced from 30% to 21%, increasing weaning from 115% to 130%. The store production system also means livestock demand is kept low during the dry period and remains low through winter. Conserved feed is now only required for 50 days compared with 100 days in the traditional system. This has reduced supplementary feed costs from $10.33/stock unit (SU) to $4.82/SU. Shifting ewes to rotationally graze lucerne in large mobs early in the growing season has decreased the stocking rate on hill country. This has allowed cover to build during each spring with promising responses from legume species.

An Integrated Methodology for Assessment and Mapping of Land Degradation Risk in Markazi Province, Iran

Desertification is recognized as a serious environmental threat in Iran because of its climatic-geomorphologicconditions. Desertification and land degradation in arid, semi-arid, and dry sub-humid regions, is a globalenvironmental problem. Accurate assessment of the status and trend of desertification is instrumental in developingglobal strategies to prevent and reverse this problem. The goal of the present study was to discover and introduce criteriaand quantitative indices and test modeling to monitor and assess desertification in the ecosystems of Iran. Past researchhas shown that effective factors for desertification can be categorized into nine groups of criteria. For each criterion istypified by a group of indices. All indices have been adjusted to natural conditions in Iran and their qualification is basedon expert knowledge and the range of natural occurrence. The Iranian model of desertification potential assessment(IMDPA) was used to evaluate desertification risk in the Farasman region in central Iran. The results show that, in spite ofcommon techniques, the proposed method has the best accuracy and produces precise results. The data were integratedover a regional geographic setting using a GIS, which facilitated data display and the development and exploration ofdata relationships, including manipulation and simulation testing. Results show that about 77% of the area fell into themoderate category, 15% fell into the low category, and the rest (8%) fell into the high category for desertification risk. Itwas found that the overall severity of land degradation and desertification in the study area has increased during thelast two decades with highly and moderately degraded land accounting for 77% of the total area in 2010. Theincorporation of natural and anthropogenic factors into the analysis provided a realistic assessment of the risk ofdesertification.

Assessment of vulnerability of Indian agriculture to rainfall variability – Use of NOAA-AVHRR (8 km) and MODIS (250 m) time-series NDVI data products

Advanced Very High Resolution Radiometer (AVHRR) (8 km) Normalized Differential Vegetation Index (NDVI) data and Moderate Resolution Imaging Spectroradiometer (MODIS) (16-day, 250m) NDVI data products were considered to analyze vulnerability of Indian agriculture to rainfall variability under climate change impact studies. Predicted higher temperature and altered rainfall patterns accompanied by extreme weather events would impact vegetation growth in natural forest, open scrub, agricultural land and plantations. NDVI derived from 2-band information (Red and Near-infra Red) of multi-spectral imagery of AVHRR (1982 to 2006) and from MODIS (20002010) were analysed to understand spatial and temporal variability. Coefficient of Variation (CV) of maximum NDVI from 15-day composites for the total length of the study period was used to assess vulnerability of rain-fed agriculture and results were corroborated with the Standard Precipitation Index (SPI) rather than actual rainfall received during the study period. AVHRR time-series data helped to identify vulnerable areas at regional-scale, i.e., agro-ecological subregions (AESR) due to coarser ground resolution while MODIS data products with 250m pixel resolution helped identify vulnerability at the district level. It was estimated that over 241 Mha areas in the country may not be vulnerable to rainfall variability-induced climate change, whereas over 81.3 Mha in arid, semi-arid and dry sub-humid regions in the country may be vulnerable to extreme weather events. Study indicated that over 12.1 and 1.81 Mha of Kharif cropland would be mildly and severely vulnerable, whereas 6.86 and 0.5 Mha of Rabi cropland may be adversely affected in a similar manner. Of the remaining agricultural lands, 29.93 and 5.24 Mha would also be vulnerable to climate change in a similar manner. Studies also indicated a decrease in length of Kharif and Rabi seasons and a delay in the start of Kharif season based on preliminary findings.

Assessment and mapping of land degradation in Abuzaydabad, Iran using an IMDPA model with emphasis on land criteria.

Land degradation, or desertification, is specific to arid, semi-arid, and dry sub-humid regions. The rate of thisphenomenon is high in developing countries such as Iran. This research investigated desertification and mapping ofdesertification in Abuzaydabad, near Kashan, Iran, with an emphasis on land criteria using an IMDPA model.Different studies have assessed land degradation or desertification and resulted in the production of different regionalmodels. The application of such models to another region requires reinvestigation of the criteria and adjustments forlocal conditions. The present study used the newest and best model for assessment. Three key regional criteria weredefined for desertification: geology-geomorphology, soil, and wind erosion. A working unit map was made using ageomorphologic method and land use in each working unit was determined. Thematic databases were integrated andenhanced using GIS and its spatial modeling function. Using the developed land degradation or desertificationmapping, it was found that of the total study area (16161 ha), medium desertification was found in 4792 ha and highdesertification was found in 11369 ha.

Perspectives in dryland restoration: approaches for climate change adaptation

Reforestation efforts in dryland ecosystems frequently encounter drought and limited soil productivity, although both factors usually interact synergistically to worsen water stress for outplanted seedlings. Land degradation in drylands (e.g. desertification) usually reduces soil productivity and, especially, soil water availability. In dry sub-humid regions, forest fires constitute a major disturbance affecting ecosystem dynamics and reforestation planning. Climate change projections indicate an increase of drought and more severe fire regime in many dryland regions of the world. In this context, the main target of plantation technology development is to overcome transplant shock and likely adverse periods, and in drylands this is mostly related to water limitations. In this paper, we discuss some selected steps that we consider critical for improving success in outplanting woody plants, both under current and projected climate change conditions including: (1) Plant species selection, (2) Improved nursery techniques, and (3) Improved planting techniques. The number of plant species used in reforestation is increasing rapidly, moving from a reduced set of well-known, easy-to-grow, widely used species, to a large variety of promising native species. Available technologies allow for reintroducing native plants and recovering critical ecosystem functions for many degraded drylands. However, climate change projections introduce large uncertainties about the sustainability of current reforestation practices. To cope with these uncertainties, adaptive restoration approaches are suggested, on the basis of improved plant quality, improved techniques for optimizing rain use efficiency in plantations, and exploring native plant species, including provenances and genotypes, for their resilience to fire and water use efficiency.

Alternatives for erosion control by using conventional coverage, non-conventional coverage and revegetation

Humankind's unsustainable behaviour regarding land-use has negative effects on the environment, leading to loss of fertility and degradation and desertification; this has a direct impact on the decline and deterioration of water resources, soil erosion and thus changes in the weather leading to drier conditions. The foregoing are caused by the misuse of soil. The way soil resources have suffered gradual deterioration has become evident in Colombia during recent years; this has been produced by erosion and the removal of mass caused by various factors including physical and chemical erosion. All the above, together with negative events such as global climate change and the sedimentation of rivers, means a negative environmental impact. Soil erosion and desertification are major environmental issues regarding disturbances and threats affecting the arid, semiarid and dry sub-humid Mediterranean region's geo-ecosystems in the third millennium; additionally, economic global change may exacerbate such problems (Ingram et al., 1996; Williams et al., 1996). Regarding soil deterioration, soil vegetation cover and erosion control and mitigation measures should be introduced by using mechanisms which should be as natural as possible and do not induce fresh impacts on the environment. This literature review has thus documented the state of the art regarding several alternatives for erosion control currently involving bioengineering.

Application of sensitivity analysis for assessment of de-desertification alternatives in the central Iran by using Triantaphyllou method

Desertification, land degradation in arid, semi-arid, and dry sub-humid regions, is a global environmental problem. With respect to increasing importance of desertification and its complexity, the necessity of attention to the optimal de-desertification alternatives is essential. Therefore, this work presents an analytic hierarchy process (AHP) method to objectively select the optimal de-desertification alternatives based on the results of interviews with experts in Khezr Abad region, central Iran as the case study. This model was used in Yazd Khezr Abad region to evaluate the efficiency in presentation of better alternatives related to personal and environmental situations. Obtained results indicate that the criterion "proportion and adaptation to the environment" with the weighted average of 33.6% is the most important criterion from experts viewpoints. While prevention alternatives of land usage unsuitable of reveres and conversion with 22.88% mean weight and vegetation cover development and reclamation with 21.9% mean weight are recognized ordinarily as the most important de-desertification alternatives in region. Finally, sensitivity analysis is performed in detail by varying the objective factor decision weight, the priority weight of subjective factors, and the gain factors. After the fulfillment of sensitivity analysis and determination of the most sensitive criteria and alternatives, the former classification and ranking of alternatives does not change so much, and it was observed that unsuitable land use alternative with the preference degree of 22.7% was still in the first order of priority. The final priority of livestock grazing control alternative was replaced with the alternative of modification of ground water harvesting.

Vegetation, water and thermal stress index for study of drought in Nepal and central northeastern India

Drought is the degradation of land in arid, semi-arid and dry sub-humid regions caused primarily by human activity and climatic variations. The present study is the first attempt to identify and monitor drought using a vegetation index, a vegetation-water index and land surface temperature (LST) data for Nepal and central northeastern India. We propose a Vegetation Water Temperature Condition Index (VWTCI) for monitoring drought on a regional scale. The VWTCI includes the Normalized Difference Water Index (NDWI), which measures the water status in vegetation, the Normalized Difference Vegetation Index (NDVI) and LST data. To validate the approach, the VWTCI was compared with the Vegetation Temperature Condition Index (VTCI) and Tropical Rainfall Measuring Mission (TRMM) 3B31 Precipitation Radar (PR) data. The study revealed a gradual increase in the extent of drought in the central part of the study area from 2000 to 2004. Certain constant drought areas were also identified and the results indicate that these areas are spreading slowly towards the northeast into the central part of the study area. Comparison of the drought areas also shows a decrease in rainfall in June and July from 2000 to 2004.

Time series analysis of optical remote sensing data for the mapping of temporary surface water bodies in sub-Saharan western Africa

A map of temporary small water bodies (TSWB) at 1 km resolution was derived for the arid, semi-arid and dry sub-humid regions of sub-Saharan western Africa where the spatio-temporal distribution of actual surface water occurrence exhibits high inter- and intra-annual variability. Water bodies and humid areas have been mapped and characterized by the analysis of 10 daily small water bodies (SWB) maps based on SPOT VEGETATION (VGT) data spanning the period January 1999–September 2007. Further analysis of the SWB time series provided additional information about the seasonal recurrence of water bodies as well as their hydrological function. A map derived from a continuous time series assures the inclusion of temporary features, a clear advantage compared to other datasets, which are based on several single date observations. The method described in this paper targets at a rapid creation of TSWB maps based on the SWB time series for different time intervals and regions.

Climate and desertification: looking at an old problem through new lenses

Global poverty, defined in almost any way, is disproportionately concentrated in the arid, semiarid, and dry subhumid regions – the drylands – of the world. We suggest that the intrinsic biophysical features of these environments, interacting with some social systems that are now no longer appropriate for the changing environment, lead to widespread situations where people living in such areas are trapped in a downward spiral of environmental degradation and loss of well‐being. Externally driven changes in both the social and physical environment, ranging from trade rules to global climate change, contribute to this syndrome. The resultant destabilization of regional climates, ecosystems, hydrological systems, and the social fabric has consequences for neighboring lands as well as the global community. A more holistic set of interventions, that engages both local and global actors, is needed to reverse these negative trends.

Sustainable development: The way for future, where are we?

Sustainable development: The way for future, where are we?

Scale issues in the governance of water storage projects

In the face of global change, which is characterized by growing water demands and increasingly variable water supplies, the equitable sharing of water and the drought proofing of rural livelihoods will require an increasing physical capacity to store water. This is especially true for the semiarid and dry subhumid regions of sub‐Saharan Africa and Asia. This paper addresses the following question: What criteria should policymakers apply in choosing between centralized storage capacity in the form of conventional large reservoirs and large interbasin water transfer schemes and decentralized and distributed storage systems in the farmers' fields and in microwatersheds and villages (tanks, microdams, and aquifers)? This exploratory paper uses an interdisciplinary framework encompassing the natural and social sciences to develop four indicators that are considered critical for understanding the biochemical, physical, economic, and sociopolitical dimensions of the scale issues underlying the research question. These are the residence time of water in a reservoir, the water provision capacity, the cost effectiveness of providing reliable access to water per beneficiary, and the equity dimension: maximizing the number of beneficiaries and compensating the losers. The procedural governance challenges associated with each indicator are dealt with separately. It is concluded that water storage and the institutional capacity to effectively administer it are recursively linked. This implies that if the scale of new storage projects gradually increases, a society can progressively learn and adapt to the increasing institutional complexity.