Annual Effective Rainfall Research Articles

Enhanced weathering for CO2 removal using carbonate-rich crushed returned concrete; a pilot study from SE Ireland

A 1.21-ha pilot study in SE Ireland investigated crushed returned concrete (CRC), applied at a rate of 7.5 tonnes/ha as a soil amendment for carbon dioxide removal (CDR) by enhanced weathering (EW) over a 10-month period. Most, but not all amended sites showed enhanced concentrations of calcium and bicarbonate in shallow soil waters compared with adjacent controls. Soil pH increased rapidly by 0.3 to >1 pH units (5.75 ± 0.25 (n = 8) in controls to 6.5 ± 0.7 (n = 24) at amended sites), with greatest increases in soils that had lowest initial pH (<6.0). Aside from one site where concentrations continued to increase, calcium (1.76–0.39 mM Ca) and bicarbonate (4.06–0.64 mM) values in soil waters declined gradually over the course of the study, consistent with rapid initial dissolution and progressive exhaustion of the fine-grained fraction, as indicated by a shrinking-core model. Most sites exhibited high bicarbonate to cation ratios (1.2–2.2) consistent with CRC dissolution by soil carbonic acid, although two sites adjacent to the field-boundary river that floods periodically showed evidence for strong acid (nitric) dissolution. Enhanced bicarbonate levels in soil waters at amended sites compared with controls, coupled with a downward-flush hydrological model driven by annual effective rainfall to calculate bicarbonate export and a simple stoichiometric correction for nitric acid weathering, indicate gross CDR rates in the range zero to 0.52 tonnes CO2/ha (69 kg CO2/tonne), limited by bicarbonate export rather than weathering rates. Further optimisation of the CDR efficiency of this material should be possible using strategies to avoid or pre-neutralise non-carbonic soil acids and by taking account of sub-aerial carbonation at the post-crushing, pre-amendment stage that arises when the material is crushed in preparation for EW applications. A simplified life-cycle analysis indicates that a discount of about 11% should be applied to account for CO2 emissions from crushing, transport and spreading operations.

Analysis of seasonal variation in the hydrological behaviour of a field combining surface and tile drainage

Agricultural drainage increases hydrological connectivity between fields and receiving environments. Tile drains and drainage ditches are the main drainage types studied at the field scale. They can be associated with temporary surface drains to improve the removal of surface water. Combining surface drains with tile drains is likely to modify surface runoff and soil water dynamics. The behaviour of tile-drained fields has been studied at the event scale, but few studies have been conducted over a full hydrological year, and no studies have quantified water volumes in a field combining surface and tile drainage. So quantifications of water partition between surface drainage, tile drainage and soil water are needed to understand the hydrological behaviour of a field combining surface and tile drains. Moreover, at the event scale, few studies showed macropores can contribute to tile drain runoff but the partition between preferential flow and matrix flow is still unclear. It needs to be study depending on several parameters as soil type, soil water content or agricultural practice for a better understanding. In this study, high temporal resolution quantification of surface runoff and tile drainage was conducted for two full hydrological years to study hydrological functioning of the field using the water balance for a drained field. Soil water pathways were studied under dry and saturated soil conditions, tracing water by measuring stable isotope (18O and 2H) concentrations in rainwater, soil water, and surface and tile runoff. Runoff quantification showed that surface drainage and tile drainage respectively transferred 44% and 20% of annual effective rainfall. However, water balance showed that, at the annual scale, 65% of infiltrating water was not captured by tile drains. At the event scale, water tracing showed a season variation in macropores contribution depending on soil hydric state. Under dry conditions, rainwater was directly transferred to tile drains, likely through macropores. On saturated soil, pre-event soil water content provided most of the water flowing out from the tile drain, but rainfall can contribute up to 25% of the water flowing out from the tile drains. Combining water balance and water trancing allowed to propose a conceptual model for surface and tile drainage hydrological functioning at the event scale.

Analysis of dry and wet weeks of rainfall by using Markov Chain - A case study at Jorhat (Assam), India

Knowledge of the weekly dry and wet spell rainfall analysis is an important aspect for successful agricultural planning as well as water conservation techniques. The rainfall data during the period 1996-2018 from Jorhat station has been analyzed and the average, maximum, minimum, standard deviation and co-efficient of variation for each 52 Standard Meteorological Weeks (SMWs) were calculated. The initial and conditional probabilities of dry and wet weeks were investigated by employing Markov Chain probability model. It was observed that, during the first 12 SMWs, the chance of two and three consecutive dry weeks was ranged from 40 to 100% and from 15 to 96%, respectively, while the chance of two and three consecutive wet weeks was ranged from 0 to 20% and 0 to 16%, respectively. The 20th SMW (14th to 20th May) is the earliest and the 23rd SMW (4th to 10th June) is the most delayed week of the onset of rainy season. Also, the 40th SMW (1st to 7th Oct) is the earliest and the 47th SMW (19th to 25th Nov) is the latest of withdrawal of southwest monsoon. The length of the rainy season is 161 days (21st May to 28th Oct). The 41st to 43rd SMWs were vulnerable to 50% probability for dryness. The monthly effective rainfall (ER) of the station was calculated and it was observed that, the total annual ER accounts only 47% of the average annual rainfall of this region.

Hydroclimatic analysis of rising water levels in the Great rift Valley Lakes of Kenya

Study RegionThe Great Rift Valley lakes of Kenya have recently experienced significant increases in their water levels, negatively impacting the local communities. This has provoked renewed concerns about the causations, with various geological, anthropogenic and hydro-climatic influences hypothesized as potential causes of the water level rises. Study FocusThis study analyses and documents water level fluctuations in Lakes Baringo, Bogoria, Nakuru, Solai, Elementaita and Naivasha. Hydrometeorological analyses are undertaken to understand potential causes and lake volume data is used to derive the “Integrated Catchment Response” (ICR), a magnitude which allows to relate changes in water balance components to signals observed in the lake volume changes. New Hydrological Insights for the RegionCompared to 1984−2009, the recent increases in lake areas range from 21 % for Lake Naivasha to an extraordinary 123 % for Lake Solai. Mean annual rainfall for 2010−2020 increased by up to 30 %. Actual evapotranspiration also increased, but to lesser extent compared to rainfall. The results illustrate that changes in catchment properties due to anthropogenic influences or changes in underground permeability are not necessary to explain the lake level rises. Based on the ICR only surprisingly minor changes in the water balance are necessary to explain the lake level rises, since an increase of only 0.4–2 % of mean annual effective rainfall leads to the observed phenomena.

Spatial-temporal trend of grassland net primary production and their driving factors in the Loess Plateau, China

Net primary productivity (NPP) of grassland is a key link and important part of the ecosystem's carbon cycle. We estimated the changes of NPP in grasslands of the Loess Plateau with unchanged land use types during 2000-2015 and analyzed its responses to the variation of main climate factors (annual precipitation, annual heavy rainfall, annual effective rainfall days, annual average temperature, annual maximum temperature, annual minimum temperature) using piecewise linear regression and Pearson correlation analysis. The driving factors of grassland NPP were further analyzed by pixel-by-pixel with boosted regression tree analysis. The results showed that annual mean grassland NPP in the Loess Plateau showed an increasing trend during the study period, with 51.3% of the total grassland area showing a significant increasing trend. The average increase rate of annual mean NPP declined from 15.23 g C·m-2·a-1 in 2000-2004 to 3.58 g C·m-2·a-1 in 2004-2015. There was a significant positive correlation between grassland NPP and precipitation, but negative correlation with temperature factors. Annual precipitation was the dominant climatic factor affecting NPP of the whole study area with the highest relative importance. Annual maximum temperature was the dominant driving force of grassland NPP of central Loess Plateau, while annual minimum temperature mainly affected the growth of grassland in high-altitude area of the western Loess Plateau.

Impact of climate variation from 1965 to 2016 on cotton water requirements in North China Plain

Climate change directly affects crop evapotranspiration and irrigation demand. The temporal and spatial variation of crop evapotranspiration is crucial to irrigation schedule planning and water resource management. Using 52 years of climate data from 43 stations in the North China Plain, this study examined trends and spatial distributions of the cotton evapotranspiration (ETc) and irrigation requirement (Iwr) and revealed the impact of climate variation on cotton ETc change. We found that, annual ETc of cotton in the growing season showed a significant declining trend, which decreased from 606 mm yr−1 in 1965-1975 to 551 mm yr−1 in 2006-2016. Annual effective rainfall (Re) and Iwr of cotton’s growing season did not show consistency over the 52 year period, which averaged at 451 mm (441∼ 466 mm) and 122 mm (105 ∼ 145 mm), respectively. The 75% of cotton ETc was supplied by rainfall and 25% by irrigation water. This is much better than for winter wheat where 60% must be supplied by irrigation. The location of the spatial maximum cotton ETc shifted during the past five decades. From 1965 to 1975, maximum ETc values were found in the southern part and then shifted to the northeastern part from 1976 to 1985. During the period of 1986 to 2005, maximum ETc occurred in the middle area and shifted to the western part in 2006-2016. During the past five decades, solar radiation, sunshine hours and wind speed decreased significantly resulting in a significant decrease in ETc at −1.1 mm yr−1. This study highlights the indispensable information of water requirements for future irrigation scheduling of cotton in the North China Plain.

Water budget components estimation for a mature citrus orchard of southern China based on HYDRUS-1D model

Minimizing the adverse impacts of soil erosion and seasonal drought are critical to sustain production for citrus orchards on red soil slopes in Southern China. Investigation of water budget between water supply and crop water demand is important to develop specific soil and water conservation measures to effectively utilize rainwater and irrigation in dry season. In this study, the surface runoff and soil water content at depths of 10 cm,20 cm, 30 cm, 40 cm, 60 cm, and 100 cm in the soil were monitored, and HYDRUS-1D model was employed to estimate the evapotranspiration and deep percolation at a mature citrus orchard in southern China. The results show that the annual effective rainfall in citrus orchards in the study area during 2010–2015 was 560.8–1071.2 mm, with an average of 812.4 mm. The average effective rainfall from April to September was more than 70 mm per month, and the total amount accounted for 66.63 % of the annual effective rainfall. Deep percolation could account for 18.85 %–65.65 % of the effective rainfall, which was the main factor affecting the effective rainfall. The water demand of citrus was 645.4–994.9 mm, with an average of 843.2 mm. The average water demand of 6 years from May to August was over 90 mm per month, accounting for 55.34 % of the whole growth period, which was the key period of citrus water demand. Seasonal water deficit may occur in both high and low rainfall years in the study area, and the frequency and degree of water shortage are prominent from July to October. According to a water demand analysis, surface runoff collected by rainwater harvesting for irrigation can satisfy the water shortage for citrus during the fruit growth period. Measures to reduce deep percolation should also be considered to increase the effective rainfall for sloping citrus orchards.

Spatiotemporal Patterns of Crop Irrigation Water Requirements in the Heihe River Basin, China

Agricultural expansion, population growth, rapid urbanization, and climate change have all significantly impacted global water supply and demand and have led to a number of negative consequences including ecological degradation and decreases in biodiversity, especially in arid and semi-arid areas. The agricultural sector consumes the most water globally; crop irrigation alone uses up more than 80% of available agricultural water. Thus, to maintain sustainable development of the global economy and ecosystems, it is crucial to effectively manage crop irrigation water. We focus on the arid and semi-arid Heihe River Basin (HRB), China, as a case study in this paper, extracting spatiotemporal information on the distribution of crop planting using multi-temporal Thematic Mapper and Enhanced Thematic Mapper Plus (TM/ETM+) remote sensing (RS) images. We estimate the spatiotemporal crop irrigation water requirements (IWRc) using the Food and Agriculture Organization of the United Nations (FAO) Penman-Monteith method and reveal variations in IWRc. We also analyze the impact of changes in crop planting structure on IWRc and discuss strategies for the rational allocation of irrigation water as well as policies to alleviate imbalance between water supply and demand. The results of this study show that effective rainfall (ER) decreases upstream-to-downstream within the HRB, while crop evapotranspiration under standard conditions (ETc) increases, leading to increasing spatial variation in IWRc from zero up to 150 mm and between 300 and 450 mm. Data show that between 2007 and 2012, annual mean ER decreased from 139.49 to 106.29 mm, while annual mean ETc increased from 483.87 to 500.38 mm, and annual mean IWRc increased from 339.95 to 370.11 mm. Data show that monthly mean IWRc initially increased before decreasing in concert with crop growth. The largest values for this index were recorded during the month of June; results show that IWRc for May and June decreased by 8.14 and 11.67 mm, respectively, while values for July increased by 5.75 mm between 2007 and 2012. These variations have helped to ease the temporal imbalance between water supply and demand. Mean IWRc values for oilseed rape, corn, barley, and other crops all increased over the study period, from 208.43, 349.35, 229.26, and 352.85 mm, respectively, in 2007, to 241.81, 393.10, 251.17, and 378.86 mm, respectively, in 2012. At the same time, the mean IWRc of wheat decreased from 281.53 mm in 2007 to 266.69 mm in 2012. Mainly because of changes in planting structure, the total IWRc for the HRB in 2012 reached 2692.58 × 106 m3, an increase of 332.16 × 106 m3 (14.07%) compared to 2007. Data show that 23.11% (76.77 × 106 m3) of this increase is due to crop transfers, while the remaining 76.89% (255.39 × 106 m3) is the result of the rapid expansion of cultivated land. Thus, to maintain both the sustainable development and ecological security of the HRB, it is crucial to efficiently manage and utilize agricultural water in light of spatiotemporal patterns in IWRc changes as well as IWRc variations between different crops. The cultivation of water-demanding crops and the further expansion of agricultural land should also be avoided.

Estimation of water requirement for different crops using CROPWAT model in Anantapur region

Groundwater exploration for irrigation is a costly and scare input in agriculture and plays an important role in increasing food production. Due to over use of groundwater resources, it has become very important to estimate the Crop Water Requirement for different crops. Unscientific and injudicious application of groundwater in the Anantapur region resulted in depletion of the groundwater table. Anantapur region was chosen as the study area as its sever water problem. To achieve effective utilization of the groundwater resources, there is a need to estimate the crop water requirement for different crops at different management levels to accomplish effective irrigation management in the Ananthapur region. It is important that the water requirements of the crops are known. This study was carried out using CROPWAT 8.0 model. The information about climatic conditions, soil types and cropping pattern were obtained in the study area to estimate the crop water requirement under rainfed condition. The crop water requirement for the different crops of Anantapur region is very essential for effective utilization of the groundwater and also to be increase the crop yield. The maximum quantity of effective rainfall observed during the month of September as 79.5 per cent of the monthly rainfall i.e. 101.7 mm and average annual effective rainfall was estimated over the period 1985 to 2012 as 85.5% of the average annual rainfall i.e. 526 mm out of 615.4 mm of average annual rainfall. The crop water requirement for the groundnut Kharif and Rabi crops in the Anantapur region was estimated as 591.3 mm and 443.3mm, respectively and for the vegetables, cotton, rice, grains and maize in the Anantapur region are to be 594.1 mm, 878.6 mm, 1110.6 mm, 699.9 mm and 679.3 mm, respectively. Efficient water management becomes crucial and critical in normal or deficit rainfall years.

Improvement of the agricultural effective rainfall for irrigating rice using the optimal clustering model of rainfall station network

In this study, the clustering method was applied to improve the usage of effective rainfall (ER) for irrigating rice paddy in the region managed by the TaoYuan Irrigation Association (TIA) of Taiwan. A total of 16 rainfall stations and rainfall data from 1981 to 2000 were used. A traditional area-weighted method (Thiessen polygons method) and an optimal clustering model of ER were evaluated and compared. The optimal clustering model of ER comprised self-organizing map (SOM), k-means (KM), and fuzzy c-means (FCM) clustering algorithms. To obtain optimal clustering data of ER, the clustering groups from two to five of SOM, KM, and FCM algorithms were determined using root-mean-squared-error. The results show that three algorithms with group numbers from two to five are adopted for the monthly optimal clustering model in different months. However, for the annual optimal model, 12 sub-models are assessed and then compared. The results show that the SOM clustering with groups three was the optimal model for annual ER. The optimal clustering model of ER provides a new procedure step in preparation of the irrigation scheduling for the TIA, and the amount irrigation water waste can be reduced from 770.1 to 22.3 mm/year. The planned ER using the optimal clustering model significantly improves the irrigation water use efficient in agricultural water management.

Structure and hydrogeological functioning of an insular tropical humid andesitic volcanic watershed: A multi-disciplinary experimental approach

Summary The aim of the study is to establish an hydrogeological scheme of the structure and the functioning of andesitic volcanic systems in the insular and humid tropical context. A watershed has been instrumented at Fefe in Guadeloupe (French West Indies) in the Lesser Antilles to measure rainfall, runoff and piezometric fluctuations between 2003 and 2006. Given the heterogeneity of the volcanic deposits, a multi-disciplinary approach has been used: a geological and an hydrogeological survey, an hydrodynamic approach (hydraulic tests and signal processing of hydrological time series), and finally, an hydrogeochemical approach (major elements and some trace elements). Two main superposed aquifer respectively in aerial deposits, and in recent nuees ardentes (glowing ash) and lava flows, as well as the underlying aquiclude (the highly weathered older substratum) were identified. At a local scale, some hydrogeological heterogeneities internal to the aquifers were highlighted and related to a polyphased building-up of the geological formations. Hydraulic relationships between the multi-layered aquifers, such as the confinement of the deep aquifer upstream of the basin, were identified. Groundwater/stream exchanges were characterised, detailing various contributions of the shallow and the deep aquifers to stream and spring waters; significant river losses were also observed. At a global scale, within such relatively permeable volcanic formations, the aquifer recharge is about 85% of the annual effective rainfall for an average rainfall year. The hydrogeological scheme appears to be coherent with a geological structure of cut-and-fill paleovalleys frequently observed in andesitic areas. Consequently, groundwater drainage axis are mainly localised in recent nuees ardentes deposits, whereas the inversion of relief characteristic of volcanic areas explains the non-superposition of surface water and groundwater divides and both surface water losses and springs. Finally, this work shows the highly heterogeneous hydrogeological processes occurring in volcanic formations of andesitic-type. It also shows the relationships between the geological structure and the hydrogeological functioning of such basins, and proposes an affordable methodological approach to investigate such a hydrogeological context in depth.

The relationship between NDVI and precipitation on the Tibetan Plateau

The temporal and spatial changes of NDVI on the Tibetan Plateau, as well as the relationship between NDVI and precipitation, were discussed in this paper, by using 8-km resolution multi-temporal NOAA AVHRR-NDVI data from 1982 to 1999. Monthly maximum NDVI and monthly rainfall were used to analyze the seasonal changes, and annual maximum NDVI, annual effective precipitation and growing season precipitation (from April to August) were used to discuss the interannual changes. The dynamic change of NDVI and the correlation coefficients between NDVI and rainfall were computed for each pixel. The results are as follows: (1) The NDVI reached the peak in growing season (from July to September) on the Tibetan Plateau. In the northern and western parts of the plateau, the growing season was very short (about two or three months); but in the southern, vegetation grew almost all the year round. The correlation of monthly maximum NDVI and monthly rainfall varied in different areas. It was weak in the western, northern and southern parts, but strong in the central and eastern parts. (2) The spatial distribution of NDVI interannual dynamic change was different too. The increase areas were mainly distributed in southern Tibet montane shrub-steppe zone, western part of western Sichuan-eastern Tibet montane coniferous forest zone, western part of northern slopes of Kunlun montane desert zone and southeastern part of southern slopes of Himalaya montane evergreen broad-leaved forest zone; the decrease areas were mainly distributed in the Qaidam montane desert zone, the western and northern parts of eastern Qinghai-Qilian montane steppe zone, southern Qinghai high cold meadow steppe zone and Ngari montane desert-steppe and desert zone. The spatial distribution of correlation coefficient between annual effective rainfall and annual maximum NDVI was similar to the growing season rainfall and annual maximum NDVI, and there was good relationship between NDVI and rainfall in the meadow and grassland with medium vegetation cover, and the effect of rainfall on vegetation was small in the forest and desert area.

The Wendover Springs record: an insight into the past and a benchmark for the future

The chalk of the English lowlands is the most important of the British aquifers. It is the principal source of water supply in much of southern and eastern England, as well as sustaining a network of chalk streams that, ecologically, are of international importance. Replenishment of the aquifer normally takes place during the winter months when evapotranspiration is low and the soil moisture deficit is negligible. In south-eastern England the margin between annual rainfall and evaporation losses is typically small and inter-annual variability in recharge totals can be very large. It is estimated that the average annual effective rainfall in the Chilterns is around 200 mm (Anon. 2003) and this modest figure – about 30% of average rainfall – is sensitive to changes in climatic conditions. Recent scenarios produced by the UK Climate Impacts Programme (Hulme et al. 2002) suggest that this sensitivity may increase if temperatures continue to rise and rainfall patterns change. Given the importance of chalk aquifers, in the context of both biodiversity and water supply, it follows that there is considerable interest in the possible impacts of climate change. Climate change scenarios are produced using increasingly sophisticated models but, given the expenditure required to address the predicted effects of climate change on water resources, policy-makers and managers will also look to the scientific community to demonstrate that there is evidence of change in observational records. The UK is blessed with extensive climatological data, with a number of temperature and rainfall records exceeding 250 years. However, with respect to the measurement of river flow, records are relatively short – the average record length held by the National River Flow Archive is less than 23 years and only 11 records exceed 70 years in length. The case for using long records is a strong one. For example, following a study of trends in UK floods, Robson (2002) concluded that a 40-year record (which exceeds that typically available) was insufficiently long to distinguish between the possible effects of climate change and natural short-term variability. Long records provide the greatest opportunity for trend identification, but a facet of their longevity is that the record is more likely to have been influenced by factors unconnected to possible changes in the climate – for example, inconsistent measurement, increasing abstraction and progressive catchment urbanisation. Consequently, it is important to establish the homogeneity of the time-series, particularly so in the case of informal records, where the data are unlikely to have been subject to the same level of scrutiny as those taken from the modern gauging network. Although there is a paucity of long records of observations that have been formally measured, reviewed and archived, there is considerable material giving contemporary accounts of historical floods and droughts awaiting discovery. The British Hydrological Society’s “Chronology of British hydrological events” (www.dundee/ geography/cbhe) is a significant step forward in locating and collating this information for public use (to date there are over 7000 entries). In addition to descriptive accounts, the river gauging authorities (principally the environment agencies) and others in the private sector (e.g. water companies) may have informal level or flow records that can usefully extend or supplement formally gauged records. This paper outlines the assembly of a unique record of flow from the Chiltern springs at Wendover, Buckinghamshire, and describes the flow patterns evident in a series of over 90 years. Globally there are few records that describe flow variability in the latter part of the nineteenth century as completely as the Wendover series and an exceptional drought episode that occurred during that era, described here, is not well documented elsewhere. The paper concludes by discussing recent events in the context of this long historical record.

Testing a climato-topographic index for predicting wetlands distribution along an European climate gradient

Knowledge of the spatial distribution of wetlands within landscapes is needed for a number of different purposes as non-point pollution control, aquatic life, flood protection or sediment traps or sources. The purpose of this paper was to propose and to test a parsimonious method for predicting wetlands in small catchments across a wide range of geological, topographic and climatic conditions. A climato-topographic index has been derived from the topographic index—taking into account the local slope and the upslope drainage area, first proposed by Beven and Kirkby [Hydrol. Sci. Bull. 24 (1979) 43]. This new index takes into account the effective rainfall, in addition to topographic factors, in order to achieve a prediction of wetland occurrence for places with different rainy conditions. The two indexes were compared. Six study areas were selected representing a wide range of climate, geology and geomorphology across Europe. The wetland area ranges from 1 to 30% of the total area for the different catchments, and the annual effective rainfall from 67 to 592 mm. The climato-topographic index seems able to predict the structure and general areal extent of wetlands without any local calibration of the model, except where the permeability of the soil surface is important and very different from the other sites considered. The climato-topographic index gives a classification of wetland occurrence similar to the field data. The exact location of the wetland is often poorly predicted, but this is mostly due to the current poor quality of the Digital Terrain Model. Thus, there is currently a technical limitation to the use of the approach advocated here.

Conceptual modeling of the impacts of climate change on karst geomorphology in the UK and Ireland

British and Irish karst environments are of geomorphological and ecological conservation value. As illustrated by a simple conceptual model, future climate change is likely to influence three key aspects of karst geomorphology, i.e. hydrology, dissolution rates and the operation of other geomorphological processes such as mass movements. However, the response of an individual karst area to these changes will depend on the magnitude and nature of regional climate change, as well as the unique geomorphological characteristics of the area. In order to illustrate the range of potential responses, five contrasting karst areas are investigated in further detail (i.e. the Burren, Cuilcagh, the Mendip Hills, Assynt and the Yorkshire Dales). For each area, an assessment is made of the sensitive aspects of the geomorphology and detailed climate predictions given for the 2020s and 2050s (using the UKCIP 1998 scenarios downscaled to the bioclimatic classes identified by the MONARCH project). All areas show an increase in winter effective rainfall, and all but the Mendip Hills show at least a modest rise in mean annual effective rainfall. The Mendip Hills karst is predicted to experience a decline in mean annual effective rainfall (up to 54%) producing an allied reduction in dissolution rates and a possible increase in vulnerability of cave deposits. Turloughs in the Burren area are likely to experience more pronounced drying out in summer, but given the minor predicted alterations in effective rainfall in the Yorkshire Dales, fragile tufa deposits are unlikely to be seriously affected. The impacts of future climate change on British and Irish karst areas need to be considered alongside the already extensive human impacts in these areas, but are unlikely to cause major geomorphic change, although impacts on sensitive landforms and allied biota may have negative effects on conservation.

Effective Rainfall in Poorly Drained Microirrigated Citrus Orchards

Effective rainfall (ER) is the portion of total rainfall that plants use to help meet their consumptive water requirements, and is an important component of water resource budgeting for irrigation. The USDA's Technical Release no. 21 (TR-21) is used to predict ER and irrigation requirements for south Florida citrus, but its accuracy is in question due to high-intensity rainfall, poorly drained soils, and partial irrigation coverage in microirrigated orchards. We evaluated the calculation of ER by TR-21 under these conditions by monitoring rainfall, irrigation, water table depth, evapotranspiration (ET), and soil water content inside and outside of the microirrigation-wetted pattern in four orchards for a total of 83 site-months. We developed a soil water budget to calculate daily water table upflux, root zone water content, water used, and ER separately for the irrigated and nonirrigated root zones. Water budget ER calculated by site ranged between −3.3% and +18.2% of TR-21 ER, with a mean of +10%. A linear correlation between water budget ER and TR-21 ER using pooled data from all four sites yielded the equation: Water Budget ER (mm) = 0.79 [TR-21 ER (mm)] + 17.7, r = 0.84. A hypothetical ER comparison using 30-yr mean rainfall and ET data showed that annual ER calculated by TR-21 amounted to 673 mm, while water budget ER totaled 744 mm, or +10.5%. We suggest that the TR-21 method has the level of accuracy needed to allocate water for microirrigated citrus on poorly drained south Florida soils.

Effective Rainfall in Poorly Drained Microirrigated Citrus Orchards

Effective rainfall (ER) is the portion of total rainfall that plants use to help meet their consumptive water requirements, and is an important component of water resource budgeting for irrigation. The USDA's Technical Release no. 21 (TR‐21) is used to predict ER and irrigation requirements for south Florida citrus, but its accuracy is in question due to high‐intensity rainfall, poorly drained soils, and partial irrigation coverage in microirrigated orchards. We evaluated the calculation of ER by TR‐21 under these conditions by monitoring rainfall, irrigation, water table depth, evapotranspiration (ET), and soil water content inside and outside of the microirrigation‐wetted pattern in four orchards for a total of 83 site‐months. We developed a soil water budget to calculate daily water table upflux, root zone water content, water used, and ER separately for the irrigated and nonirrigated root zones. Water budget ER calculated by site ranged between −3.3% and +18.2% of TR‐21 ER, with a mean of +10%. A linear correlation between water budget ER and TR‐21 ER using pooled data from all four sites yielded the equation: Water Budget ER (mm) = 0.79 [TR‐21 ER (mm)] + 17.7, r = 0.84. A hypothetical ER comparison using 30‐yr mean rainfall and ET data showed that annual ER calculated by TR‐21 amounted to 673 mm, while water budget ER totaled 744 mm, or +10.5%. We suggest that the TR‐21 method has the level of accuracy needed to allocate water for microirrigated citrus on poorly drained south Florida soils.

Estudo da precipitação efetiva para o município de Lavras, MG

A determinação da precipitação efetiva apresenta grande relevância no estudo da precipitação com fins de aplicação na agricultura, visto que esta parcela da precipitação é realmente aquela que estará contribuindo com a água disponível do solo. Em conseqüência, sua quantificação é de grande utilidade nas irrigações suplementares, levando o irrigante a alcançar expressiva economia na condução da irrigação. O objetivo deste trabalho foi realizar um estudo de chuva efetiva mensal, utilizando-se as precipitações prováveis mensais estimadas por meio da distribuição Log-Normal, com dados observados junto à estação climatológica da Universidade Federal de Lavras, no período de 1914 a 1991, para o município de Lavras, MG. Foram utilizados os seguintes métodos para se estimar a precipitação efetiva: percentagem fixa (PF), fórmula empírica (AGLW/FAO) e o do Soil Conservation Service Method (USDA). Considerando-se o nível de probabilidade de 75%, foram encontrados valores de precipitação efetiva anual de 125,4, 313,6, 501,8, 330,6 e 485,0 mm para os métodos PF 20, 50 e 80%, FAO e USDA, respectivamente. Para o nível de probabilidade de 90%, encontraram-se os menores totais anuais de precipitação efetiva, sendo: 79,5, 198,8, 318,1, 188,8 e 327,8 mm para os métodos PF 20, 50 e 80%, FAO e USDA, respectivamente.