Long-term Average Rainfall Research Articles

Targeting Trachoma Control through Risk Mapping: The Example of Southern Sudan

BackgroundTrachoma is a major cause of blindness in Southern Sudan. Its distribution has only been partially established and many communities in need of intervention have therefore not been identified or targeted. The present study aimed to develop a tool to improve targeting of survey and control activities.Methods/Principal FindingsA national trachoma risk map was developed using Bayesian geostatistics models, incorporating trachoma prevalence data from 112 geo-referenced communities surveyed between 2001 and 2009. Logistic regression models were developed using active trachoma (trachomatous inflammation follicular and/or trachomatous inflammation intense) in 6345 children aged 1–9 years as the outcome, and incorporating fixed effects for age, long-term average rainfall (interpolated from weather station data) and land cover (i.e. vegetation type, derived from satellite remote sensing), as well as geostatistical random effects describing spatial clustering of trachoma. The model predicted the west of the country to be at no or low trachoma risk. Trachoma clusters in the central, northern and eastern areas had a radius of 8 km after accounting for the fixed effects.ConclusionIn Southern Sudan, large-scale spatial variation in the risk of active trachoma infection is associated with aridity. Spatial prediction has identified likely high-risk areas to be prioritized for more data collection, potentially to be followed by intervention.

Phenological study on a tropical secondary forest in West Sumatra, Indonesia

We made litter fall observations in a West Sumatran tropical rain forest every 2 weeks through 3 years (including the drought year, 1997). Seasonal changes in long-term average rainfall were bimodal, but even in the two dry seasons average monthly precipitation was > 200 mm. Leaf-fall rates in a year with normal rainfall peaked in the first dry season; leaves made up one-third of mean annual litter fall. Larger trees had highly synchronized leaf fall during the peak shedding period. Smaller trees shed simultaneously during severe drought. Twigs

Groundwater–surface water interaction and the impact of a multi-year drought on lakes conditions in South-East Australia

South-East Australia is currently experiencing a severe multi-year drought (not, vert, similar11 years of below long-term average rainfall between 1997 and 2008). To refine our understanding of the impacts of such climate stresses on lake systems, and to overcome the limitations of insufficient field based measurements, lake water levels and lake salinity values are combined with remote sensing data (Landsat-5TM) to analyse water and solute budgets for two large lakes in the Corangamite catchment. For these two lakes, data during pre-drought (1992–1996) and drought (1997–2006) periods are used to investigate the impact of the drought on lake and groundwater interaction and possible changes in mechanisms controlling the salinity of the lakes. For 26 other lakes in the Corangamite catchment with limited or no on-ground data, water and evaporite mapping using remote sensing data (Landsat-5TM) were used as proxies for drought impacts on lake quantity and salinity. Within the study area, this drought has resulted in a 60% loss of lakes area inundated (220 × 106 m2), and for the two largest lakes the water loss equates to an 80% decrease in volume (714 × 106 m3). Although the lakes are groundwater-fed, the rapid declines in lake water levels have not resulted in systematic increases in groundwater discharge to lakes across the study region. The lakes that are most sensitive to changes in the hydrologic budget within the catchment (10 of the 28 monitored lakes) have changed from groundwater throughflow or discharge lakes to intermittent recharge lakes. The decrease in lake levels is accompanied by an increase in lake salinity, however the dominant controls on increases in salinity varies for different lakes between just evaporation, and evaporation plus episodes of increased net groundwater discharge. The drought has exacerbated pre-existing high lake salinity levels; by 2006 one quarter of the lakes have evaporites where previously (before 1997) these lakes were evaporite free. These observations on changes in lakes quantity, interaction with groundwater, and salinity highlights the spatial variability in the lakes response to regional drought impacts.

Faecal near infrared reflectance spectroscopy estimates of diet quality and responses to nitrogen supplements by cattle grazing Bothriochloa pertusa pastures

A grazing experiment in the seasonally dry tropics of north Queensland examined the diet selected and the growth responses of Bos indicus steers to urea supplement over two dry seasons and one wet season, from August 2001 to January 2003. There were two groups of 10 steers (control and urea-supplemented) and each group comprised two age cohorts, A and B, of five steers each with an age difference of ~1 year. In June 2002, cohort A steers were replaced with steers 2 years younger (cohort C). The steers grazed Bothriochloa pertusa pastures on a low fertility Red Chromosol soil. The groups were switched between two adjoining paddocks at fortnightly intervals when they were weighed and faecal samples were collected for faecal near infrared reflectance spectroscopy (F.NIRS) estimates of diet quality and growth rate. Rainfall and diet quality followed the expected seasonal pattern, but the 2001–02 wet season was very short (November–January) with only 65% of the long-term average rainfall. There was no rain during the 2001 dry season (DS-1) from August to mid November, and no effective rain (17 mm) between February and December 2002. Non-grass (i.e. herbaceous dicot plants) made only a small contribution to the diet, averaging 13%. In DS-1 and in the dry season of 2002 (DS-2) diet crude protein (CP) averaged 2.5% and 2.9%, and DMD/CP (ratio of dry matter digestibility to CP) averaged 18.6 and 17.1, respectively. Liveweight (LW) loss in control steers during DS-1 averaged 32 kg. Urea supplement reduced LW loss by 18 kg (P < 0.001), but most of the benefit was lost during the following growing season. During the extended dry period in 2002, average LW losses of control steers were 85 and 47 kg in the older and younger cohorts, respectively, and supplementation with urea reduced weight losses by 53 and 31 kg, respectively (P < 0.001). F.NIRS predicted the cumulative LW of the unsupplemented steers in cohorts A and B with acceptable accuracy, the difference between the observed and predicted final LW being 6 kg for cohort A after 10 months, 12 kg for cohort B after 17 months, and 27 kg for cohort C after 7 months. The results demonstrated that F.NIRS can be effectively used to monitor dietary CP and DMD levels in grazing cattle, to help develop an understanding of cattle responses to urea supplement relative to the quality of the basal forage diet, and to provide useful decision support information for the nutritional management of grazing cattle.

DIETS OF ADULTS AND LAMBS OF DESERT BIGHORN SHEEP DURING YEARS OF VARYING RAINFALL IN CENTRAL ARIZONA

Abstract Effects of unpredictable, variable rainfall in arid systems on diets of adults and lambs of desert bighorn sheep (Ovis canadensis) are poorly understood. We determined associations based on analysis of feces between amounts of rainfall and composition and similarity (overlap and diversity) of diets of adults and lambs, and relationships between diets of adults and lambs, in the Sonoran Desert of central Arizona during 1999–2003. Drought occurred in 2 of 3 years during sampling of feces of adults, and in 1 of 3 years during sampling of feces of lambs. Composition and diversity of diets of adults were comparable during years of drought and normal rainfall, except that diets were not correlated between years when severe drought (31% of long-term average rainfall) followed normal rainfall. Composition and diversity of diets of lambs also were independent of amounts of rainfall, but dietary overlap between and within age groups was greater during years of increasing rainfall compared to previous years...

Improved soil moisture balance methodology for recharge estimation

Estimation of recharge in a variety of climatic conditions is possible using a daily soil moisture balance based on a single soil store. Both transpiration from crops and evaporation from bare soil are included in the conceptual and computational models. The actual evapotranspiration is less than the potential value when the soil is under stress; the stress factor is estimated in terms of the readily and total available water, parameters which depend on soil properties and the effective depth of the roots. Runoff is estimated as a function of the daily rainfall intensity and the current soil moisture deficit. A new concept, near surface soil storage, is introduced to account for continuing evapotranspiration on days following heavy rainfall even though a large soil moisture deficit exists. Algorithms for the computational model are provided. The data required for the soil moisture balance calculations are widely available or they can be deduced from published data. This methodology for recharge estimation using a soil moisture balance is applied to two contrasting case studies. The first case study refers to a rainfed crop in semi-arid northeast Nigeria; recharge occurs during the period of main crop growth. For the second case study in England, a location is selected where the long-term average rainfall and potential evapotranspiration are of similar magnitudes. For each case study, detailed information is presented about the selection of soil, crop and other parameters. The plausibility of the model outputs is examined using a variety of independent information and data. Uncertainties and variations in parameter values are explored using sensitivity analyses. These two case studies indicate that the improved single-store soil moisture balance model is a reliable approach for potential recharge estimation in a wide variety of situations.

Effect of mulch, irrigation, and soil type on water use and yield of maize

Tillage practices that maintain crop residues on the soil surface help reduce evaporation of soil water, which can benefit high water use crops such as maize ( Zea mays L.). Management practices, climatic conditions, and soil type may affect how well a crop responds to surface residue. We conducted experiments with short season maize in 1994 and 1995 in Bushland, TX, USA, utilizing a rain shelter facility that has lysimeters containing monolithic cores of the Pullman (fine, mixed, thermic Torrertic Paleustolls), the Ulysses (fine-silty, mixed, mesic Aridic Haplustolls), and the Amarillo (fine-loamy, mixed, thermic Aridic Paleustalfs) soil series. In 1994, the treatments were a flat wheat ( Triticum aestivum L.) straw and coconut ( Cocus nucifera L.) fiber mulch of 4 Mg ha −1 with infrequent irrigations totaling 25% and 75% of long-term average rainfall for the growing season (200 mm). The 1995 treatments were similar, but used a heavier mulch of 6.7 Mg ha −1 and more frequent irrigations totaling 60% and 100% of long-term average rainfall. The mulch was applied at the 3-leaf growth stage. Mean potential grass reference evapotranspiration for the vegetative and reproductive growth stages in 1994 was 6.6 and 6.3 mm day −1, respectively, and in 1995 it was 6.8 and 7 mm day −1, respectively. The mulched and bare soil surface treatments used similar amounts of water in each year. In 1994, mulch did not affect yield, yield components, or leaf area index (LAI). No significant differences occurred in plant available water (PAW) between mulched and bare soil treatments from emergence through harvest. In 1995, mulch increased grain yield by 17%, aboveground biomass by 19%, and grain water use efficiency (WUE) by 14% compared with bare soil treatments. Mulched treatments also maintained significantly greater PAW compared with bare soil treatments until near anthesis and, after anthesis, LAI was significantly greater in the mulched treatments compared with the bare soil treatments. In 1995, mulch significantly increased grain yield and grain WUE of the maize crop in the Pullman soil, grain yield and biomass WUE of the crop in the Amarillo soil, and had no significant effect on the crop in the Ulysses soil compared with the bare soil treatments. The significant increase in water use efficiency in 1995 was the result of soil water being used for crop growth and yield rather than in evaporation of soil water. The more favorable soil water regime in 1995 compared with 1994 between the mulched and bare soil treatments was possibly due to the higher evaporative demand environment, the increase in mulch mass, and the increased irrigation frequency. This was especially important in soils where textural characteristics affected both rooting and soil water extraction by maize which limited its ability to tolerate water stress.

Biomass production of different ecotypes of threegrass species of the semi-arid grasslands of southern Africa

Biomass production of different ecotypes within three ecological importantgrass species was determined during cultivation under uniform environmental conditions. Results obtained clearly indicate that ecotypes of these species exhibit a significant degree of variation with regard to biomass production. Furthermore, indications from this investigation are that no correlation exists between production ability of a species and long-term average rainfall, and the effect of both genetic and environmental factors on the production ability of a species determines the eventual biomass production of a species. Biomass production represents one of various ecologically important characteristics to be used in conjunction with other ecological characters to construct a usable, special purpose classification system. This system will assist rangeland ecologists in identifying functional ecotypes within grass species, thus facilitating the understanding and interpretation of vegetation dynamic models and rangeland condition assessments.

Phenotypic divergence for morphological and yield-related traits among landrace genotypes of durum wheat from Jordan

Landrace genotypes of durum wheat, from 10 districts in Jordan, have been evaluated for 18 morphological and yield related traits. Results of multivariate analysis, including analysis of variance, cluster analysis and canonical discriminant analysis, indicate that the magnitude of phenotypic divergence in these landrace genotypes is large, especially when compared with a world collection of durum wheat. These results provide an experimental evidence for phenotypic differentiation as a result of variation in altitude and long-term average rainfall of collection sites, but not on the basis of district of collection. R2-values for fit to least squares model ranged from 67.0–78.0%, and from 18.5–30.0%, for the first and second cases, respectively. Landrace genotypes from different districts formed 5 clusters on the basis of altitude and long-term average rainfall of collection site. Three canonical factors accounted for 92% of total variance in these clusters. The first canonical factor accounted for 57% of total variance and was mainly correlated with spike length, awn length and spikelets/spike. The second canonical factor accounted for 22% of total variance and was positively correlated with peduncle length, seed weight per plant, kernel weight and ratio of peduncle length to plant height. However, it was negatively correlated with awn length. The phenotypic diversity found in these landrace genotypes could help identify genetically different genotypes for durum wheat improvement.

Lucerne survival in south-east Queensland in relation to grazing management systems

Survival of lucerne plants and changes in the row cover of lucerne in relation to grazing management were studied in an experiment at Lawes, south-east Queensland, from 1971 to 1977. There were six grazed treatments (resting for 32 or 44 days combined with grazing for 4 or 16 days, resting for 56 days with grazing for 4 days, and resting for 40 days with grazing for 8 days) and three mown treatments (mown every 36,48 or 60 days). All grazing was with sheep, at a stocking rate equivalent to 20 ha-1 on a year round basis. The experiment was irrigated when necessary to ensure that moisture at least equivalent to the long-term average monthly rainfall was received. There were about 42 lucerne plants m-2 in November 1971 and about 13 plants m-2 in October 1977; thus lucerne survival was good in all treatments, with stands losing about five plants m-2 annum-1. Management effects were small, with survival and row cover becoming slightly better as the interval between grazings or mowings increased from 32 to 60 days. Grazing for four days gave poorer survival than either grazing for 8 or 16 days or mowing. Perennial grass cover was much greater with four-day grazing than in the other treatments. Inspection at the end of the experiment showed nearly all crowns to have moderate symptoms of crown rot caused by Colletotrichum trifolii. The need for critical attention to the interaction between moisture supply, grass invasion and disease accumulation in maintaining lucerne stands in sub-tropical environments is discussed.

The spottiness of rainfall in a desert area

Between one half and two thirds of the total rainfall in the southernmost, arid part of Israel is of a highly localized type, coming mostly from small convective cells. In a number of storms, the dimensions of such cells could be estimated; the typical diameter was about 5 km. Larger localized systems exist as well. In the instances observed, cells mostly appeared well-separated from each other, both in time and space. Consequently, in a region (or a watershed) of a few hundreds of sq. km., the proportion of the area receiving intensive rainfall on a given day may be as low as 20%. The area covered by individual cells seems to be randomly distributed in space, as long-term average rainfall is uniform throughout the region considered. The number of days on which rain occurs somewhere within that region, is about 50% higher than the number recorded at any single point. Correlation analysis has been used to compare the degree of spottiness in this area and in other climatic regimes. Seasonal differences have also been found. Spottiness is most pronounced in the fall and late spring, whereas spatially uniform rainfall is most likely to occur in mid-winter.

Summer weather conditions and wheat stem rust in the Dakotas, Nebraska, and Minnesota

June and July temperature and rainfall data for the U.S. Weather Bureau stations located in the spring wheat areas of the Dakotas, Minnesota and Nebraska were related to wheat stem rust severity in those states during 1904–60. In all the states, more of the June and July temperature averages of the severe rust years were below the 57-year average temperature. The majority of the June and July rainfall averages of the severe years were above the 57-year average rainfall. The analyses indicated that the long-term average temperature and rainfall lines were not precise in separating rust from no-rust years over a 57-year period;however, they might have some value until more exact criteria are found.