Water Requirement Satisfaction Index Research Articles

Rainfall analysis for rain-fed farming in the Great Rift Valley Basins of Ethiopia

AbstractRainfall is the most important source of water for crop production in Ethiopia. However, its temporal and spatial variability is leading to serious food shortages and insecurity in the country. This study was aimed at investigating the characteristics of selected agroclimatic variables over the great Rift Valley regions of Ethiopia. Long term (1981–2010) climate data were analyzed for 17 stations selected based on agroecology representation. Selected descriptors for climate variability and the Mann–Kendall trend test were employed. Onset, cessation, length of growing period (LGP), water requirement satisfaction index and dry spell occurrence during the growing period were determined. The results showed low to very high rainfall variability (14–35%), LGP (20–256 days) and dry spell probability (50–100%) during the main season. Significant (P ≤ 0.05) annual and seasonal rainfall trends were observed in some stations. The probability of occurrence of a dry spell during the seasons was found to be a challenge for most of the stations in the mid and low altitude areas of the basins. Consequently, seasonal water deficit was observed in these areas which hampered crop production. Area specific recommendations are thus required based on specific challenges in the study region.

Potential area and limitations for the expansion of rainfed wheat in the Cerrado biome of Central Brazil

Abstract: The objective of this work was to locate and quantify, through geotechnologies, areas that are currently used for annual agriculture in the Cerrado biome of Central Brazil, located within the boundaries defined by the homogeneous region of adaptation of wheat cultivars 4 and that present favorable conditions for rainfed wheat (Triticum aestivum) cultivation. The following information layers were crossed: use and coverage of the Cerrado biome, digital elevation model, and water requirement satisfaction index for wheat in the Cerrado biome. In addition, different levels of water stress (low, moderate, and high), risk levels (20, 30, and 40%), available soil water capacities (ASWCs) (35, 55, and 75 mm), cultivar cycles (105, 115, and 125 days), and sowing dates (in February and March) were also considered. A greater favorable area was observed for sowing in early February, and group I of cultivars (105 days) presented the greatest favorable area. Above 800 m altitude, 2.7 million hectares were classified as favorable for the best combination of factors, i.e., sowing on February 5, ASWC of 75 mm, 105-day cycle, 20% risk level, and low and moderate impacts.

Analysis of potential future droughts limiting maize production, in the Luvuvhu River catchment area, South Africa

Recurring droughts associated with global warming have raised major concern for the agricultural sector, particularly vulnerable small-scale farmers who rely on rain-fed farming such as in the Luvuvhu River catchment. The Standardized Precipitation Evapotranspiration Index (SPEI) and Water Requirement Satisfaction Index (WRSI) were calculated to assess drought on a 120-day maturing maize crop based on outputs of the CSIRO-Mk3.6.0 under RCP 4.5 emission scenario, for the period 1980/81–2089/90. Results by SPEI show that 40–54% of the agricultural seasons during the base period experienced mild drought conditions (SPEI 0 to −0.99), equivalent to a recurrence of once in two seasons. However, WRSI results clearly indicated that stations in the drier regions (annual rainfall <600 mm) of the catchment experienced mild drought (WRSI 70 - 79) corresponding to satisfactory crop performance every season. Results further showed overall mild to moderate droughts in the beginning of the near-future climate period (2020/21–2036/37) with SPEI values not decreasing below −1.5. These conditions are then expected to change during the far-future climate period (2055/56–2089/90), whereby results on the expected crop performance predicted significantly drier conditions (p < 0.05). This study provided information on how farmers in the area can prepare for future agricultural seasons, while there is sufficient time to implement strategies to reduce drought risk potential. Thus, integrated interventions could provide best options for improving livelihoods and building the capability of farmers to manage climate change-related stresses.

Zoning of water requirement satisfaction index for common bean in Mato Grosso

ABSTRACT The aim of this study was the agroclimatic zoning of common bean in the Mato Grosso state in the second harvest. Data from 38 meteorological stations in the state and in neighboring regions were used. The zoning was based on water requirement satisfaction index (WRSI) for the common bean crop, for the three levels of available water capacity of the soils of the state (30, 50 and 75 mm) in 12 sowing periods. After generating the indexes for the municipalities, the variograms of the data were fitted in order to enable interpolation of the data for the state. Data were entered into ArcGISTM 10.0 and the ordinary kriging interpolation method was used. After generating the maps, they were clipped to the Mato Grosso State and classified as the following WRSI classes: suitable (WRSI ≥ 0.65); restricted (0.55 &lt; WRSI &lt; 0.65) and unsuitable (WRSI ≤ 0.55) for the stage of flowering and grain filling. It was possible to interpolate only the ten-day periods 8 to 12, because from 1 to 7 all regions of the state are suitable for cultivation. The trend of the aptitude of sowing dates is similar to the movement of the air masses active in the state, with a northwest-southeast direction of displacement.

Rangeland water requirement satisfaction index under rainfall variability and predicting future rainfall scenarios: implication for availability of feed resources

IntroductionRangeland ecosystems provide multiple ecosystem services, including feed resources for wild and domestic herbivores in semi-arid areas. However, under the ever increasing environmental changes, the impact of rainfall variability on the productivity and vegetation dynamics of rangelands are the great challenges that pastoral community are facing today. As a result, the potentials of most rangelands in semi-arid ecosystems affect the livestockproduction. Therefore, we studied the interconnections between the long-term rainfall variation and the rangeland Water Requirement and Satisfaction Index (WRSI) in Mieso, Jigjiga, and Shinile districts under pastoral conditions of Ethiopia.MethodsThe base period rainfall data (1984–2015) was obtained from the National Meteorological Agency of Ethiopia, whereas the future rainfall trend was predicted using MarkSim software (Representative Concentration Pathways 4.5 GHG concentration trajectory). Mann-Kendall’s statistical tests, coefficient of variation, LEAP software (version 2.61), and Minitab Software (version 15) were used to assess the relationship between rangeland WRSI and long-term rainfall variability.ResultsThe result indicated that mean annual rainfall anomaly had strong positive correlation with rangeland WRSI in Mieso (P < 0.05), Jigjiga (P < 0.001), and Shinile (P < 0.001) pastoral areas. Similarly, short and long rainy seasons had positive association (P < 0.001) with rangeland WRSI, especially in Jigjiga and Shinile pastoral districts. The base period rainfall as well as the predicted annual rainfall showed variability in amount and distribution in all studied districts in pastoral areas of Ethiopia.ConclusionsThe mean annual rainfall anomaly is correlated with the rangeland WRSI. Moreover, the future rainfall trend analysis indicated that variability of rainfall would be expected in between the years 2020–2049, 2040–2069, and 2070–2099. Thus, the future rainfall variability would limit future rangeland WRSI under pastoral conditions of Ethiopia. Based on our study, we suggested establishment and implementation of early warning systems to reduce the likely impact of rainfall variability on future rangeland potential in dry lands under the pastoral production systems in eastern Ethiopia.

Crop water budgeting for rainfed cotton for crop planning and management in Coimbatore

Analysis of water balance components was carried out for cotton crop in Annur block of Coimbatore district (11o 14´ to 11o 23´ N latitude and 77o 08´ to 77o 13´E longitude)based on the soil information (1:50, 000scale) and thirty years (1975-2005) climatic data.Soil moisture availability index showed that 37th standard week was found to be highly suitable for taking up cotton sowing due to assured rainfall. The water requirement satisfaction index indicated that about 87 per cent of the crop water requirement is satisfied by the soil moisture in the control section irrespective of soil type. The crop will facemoisture deficit from 4th to 8th standard weeks which coincide with harvesting stage.

English

The objective of this study was to accomplish an agro-climatic zoning for the Agreste region of Pernambuco State, Brazil, with the aim to identify agro-climatic zones for citrus cultivation. Monthly climatic data of 100 stations from over 20-year observation series (1911 to 1990) were selected within and close to the study area. From climatic data of mean air temperature and rainfall, we calculated the climatic water balances using available water capacity (AWC) of 50 and 100 mm. From data of both potential and estimated actual evapotranspiration, agro-climatic zones were established in agreement with the Water Requirement Satisfaction Index (WRSI). According to our study, the annual temperature variation in the Agreste mesoregion of Pernambuco State, with minimum temperature of 16.4°C and maximum of 33.4°C, is not a limiting factor for citrus production. Fifty municipalities in the region are located in the favorable agro-climatic zone for citrus cultivation, what represents an area of 12,000 km2 yet to be explored since less than 0.5% of it is being cultivated. Other 16 municipalities are located in the intermediate zone, with moderate risk, while five of them are in the adverse zone, presenting high climatic risk and water deficit. Key words: Citrus production, temperature, water balance, orange, tropical region.

Zoneamento agroclimático de amendoinzeiro para a Bacia do Alto Paraguai (MT)

RESUMO O sucesso de uma agricultura tecnificada, produtiva e sustentável é obtido por meio do conhecimento do clima e solo da localidade, combinado com o seu adequado manejo. Este estudo objetivou determinar o zoneamento agroclimático da cultura do amendoim para a região da Bacia do Alto Paraguai, no Estado de Mato Grosso, identificando os municípios que apresentam aptidão para a exploração dessa cultura e estabelecendo as épocas para a sua semeadura. Foram analisadas as condições edafoclimáticas da região, respeitando-se o ciclo (90-120 dias) e as exigências hídricas (400-600 mm) da cultura. Para os tipos de solos classificados de acordo com o teor de argila, foram determinados a capacidade de armazenamento de água (CAD) e o índice de satisfação e necessidade de água (ISNA). Concluiuse que todos os municípios que cultivam amendoim apresentam mais que 50 % de solo tipo CAD 75, com mais de 35 % de argila (Arenápolis, Barra do Bugres, Indiavaí, Lambarí D’Oeste, Nova Olímpia, Rondonópolis, São José dos Quatro Marcos e Tangará da Serra). Esse tipo de solo favorece o cultivo tardio, que pode ser realizado até o 7º decêndio. Já para os solos tipo CAD 30, com menos de 15 % de argila, o cultivo só deve se iniciar a partir do 6º decêndio, por apresentarem baixa capacidade de absorção de água.

Calculating Crop Water Requirement Satisfaction in the West Africa Sahel with Remotely Sensed Soil Moisture

Abstract The Soil Moisture Active Passive (SMAP) mission will provide soil moisture data with unprecedented accuracy, resolution, and coverage, enabling models to better track agricultural drought and estimate yields. In turn, this information can be used to shape policy related to food and water from commodity markets to humanitarian relief efforts. New data alone, however, do not translate to improvements in drought and yield forecasts. New tools will be needed to transform SMAP data into agriculturally meaningful products. The objective of this study is to evaluate the possibility and efficiency of replacing the rainfall-derived soil moisture component of a crop water stress index with SMAP data. The approach is demonstrated with 0.1°-resolution, ~10-day microwave soil moisture from the European Space Agency and simulated soil moisture from the Famine Early Warning Systems Network Land Data Assimilation System. Over a West Africa domain, the approach is evaluated by comparing the different soil moisture estimates and their resulting Water Requirement Satisfaction Index values from 2000 to 2010. This study highlights how the ensemble of indices performs during wet versus dry years, over different land-cover types, and the correlation with national-level millet yields. The new approach is a feasible and useful way to quantitatively assess how satellite-derived rainfall and soil moisture track agricultural water deficits. Given the importance of soil moisture in many applications, ranging from agriculture to public health to fire, this study should inspire other modeling communities to reformulate existing tools to take advantage of SMAP data.

Sensitivity of tree ring growth to local and large-scale climate variability in a region of Southeastern Brazil

We explored the relationship between tree growth in two tropical species and local and large-scale climate variability in Southeastern Brazil. Tree ring width chronologies of Tectona grandis (teak) and Pinus caribaea (Caribbean pine) trees were compared with local (Water Requirement Satisfaction Index—WRSI, Standardized Precipitation Index—SPI, and Palmer Drought Severity Index—PDSI) and large-scale climate indices that analyze the equatorial pacific sea surface temperature (Trans-Nino Index-TNI and Nino-3.4-N3.4) and atmospheric circulation variations in the Southern Hemisphere (Antarctic Oscillation-AAO). Teak trees showed positive correlation with three indices in the current summer and fall. A significant correlation between WRSI index and Caribbean pine was observed in the dry season preceding tree ring formation. The influence of large-scale climate patterns was observed only for TNI and AAO, where there was a radial growth reduction in months preceding the growing season with positive values of the TNI in teak trees and radial growth increase (decrease) during December (March) to February (May) of the previous (current) growing season with positive phase of the AAO in teak (Caribbean pine) trees. The development of a new dendroclimatological study in Southeastern Brazil sheds light to local and large-scale climate influence on tree growth in recent decades, contributing in future climate change studies.

A seasonal agricultural drought forecast system for food-insecure regions of East Africa

Abstract. The increasing food and water demands of East Africa's growing population are stressing the region's inconsistent water resources and rain-fed agriculture. More accurate seasonal agricultural drought forecasts for this region can inform better water and agropastoral management decisions, support optimal allocation of the region's water resources, and mitigate socioeconomic losses incurred by droughts and floods. Here we describe the development and implementation of a seasonal agricultural drought forecast system for East Africa (EA) that provides decision support for the Famine Early Warning Systems Network's (FEWS NET) science team. We evaluate this forecast system for a region of equatorial EA (2° S–8° N, 36–46° E) for the March-April-May (MAM) growing season. This domain encompasses one of the most food-insecure, climatically variable, and socioeconomically vulnerable regions in EA, and potentially the world; this region has experienced famine as recently as 2011. To produce an "agricultural outlook", our forecast system simulates soil moisture (SM) scenarios using the Variable Infiltration Capacity (VIC) hydrologic model forced with climate scenarios describing the upcoming season. First, we forced the VIC model with high-quality atmospheric observations to produce baseline soil moisture (SM) estimates (here after referred as SM a posteriori estimates). These compared favorably (correlation = 0.75) with the water requirement satisfaction index (WRSI), an index that the FEWS NET uses to estimate crop yields. Next, we evaluated the SM forecasts generated by this system on 5 March and 5 April of each year between 1993 and 2012 by comparing them with the corresponding SM a posteriori estimates. We found that initializing SM forecasts with start-of-season (SOS) (5 March) SM conditions resulted in useful SM forecast skill (&gt; 0.5 correlation) at 1-month and, in some cases, 3-month lead times. Similarly, when the forecast was initialized with midseason (i.e., 5 April) SM conditions, the skill of forecasting SM estimates until the end-of-season improved (correlation &gt; 0.5 over several grid cells). We also found these SM forecasts to be more skillful than the ones generated using the Ensemble Streamflow Prediction (ESP) method, which derives its hydrologic forecast skill solely from the knowledge of the initial hydrologic conditions. Finally, we show that, in terms of forecasting spatial patterns of SM anomalies, the skill of this agricultural drought forecast system is generally greater (&gt; 0.8 correlation) during drought years (when standardized anomaly of MAM precipitation is below 0). This indicates that this system might be particularity useful for identifying drought events in this region and can support decision-making for mitigation or humanitarian assistance.

Risco climático da cana-de-açúcar cultivada na região nordeste do Brasil

Este estudo avalia os impactos das alterações climáticas sobre o zoneamento agrícola de risco climático da cultura da cana-de-açúcar cultivada na região Nordeste do Brasil, baseado nos relatórios do IPCC. Combinado com técnicas de geoprocessamento (SIG) o modelo de balanço hídrico foi utilizado para identificar as áreas da região de estudo nas quais a cultura poderá sofrer restrições de rendimento devido às mudanças climáticas. Os dados utilizados no estudo foram as séries históricas de precipitação com no mínimo 30 anos de dados diários, coeficientes de cultura, evapotranspiração potencial e duração do ciclo da cultura. Adotou-se, como critério de corte para o Índice de Satisfação das Necessidades de Água para a cultura (ISNA) definido como a relação entre a evapotranspiração real e a evapotranspiração máxima (ETr/ETm) o valor 0,65. Os cenários utilizados nas simulações sem aumento na temperatura do ar e com aumento de 1,5; 3 e 5 ºC foram associados às alterações na precipitação de ±10, ±25 e ±40%. Os resultados indicam que existe uma diferença relevante entre os cenários de aquecimento e as condições climáticas atuais, em termos dos efeitos projetados da variação de temperatura sobre as áreas cultivadas com a cana-de-açúcar na região de estudo.

Evolution of crop yields in different tillage and cropping systems over two decades in southern Brazil

In the last three decades, the no-tillage system (NT) has provided environmental and economic advantages for farming in southern Brazil, especially when associated with crop rotation. The objective of this study was to evaluate the effects of different tillage and cropping systems on the grain yields of soybean, maize and wheat, in a 23-year experiment established on an Oxisol in the southern region of Brazil. The experiment was carried out in randomized block experimental design with four replications. The treatments consisted of three tillage systems [NT, NT with chiseling every three years (NTC), and conventional tillage (CT)] and two cropping systems [an annual crop sequence with wheat in the winter and soybean in the summer, designated as crop succession (CS), and a 4-year crop rotation with the following species in winter–summer, respectively: white lupine–maize; black oat–soybean; wheat–soybean; and wheat–soybean (CR)]. Soybean yields were correlated to the water requirement satisfaction index (WRSI) estimated for the soybean reproductive period. With few exceptions, the NT showed higher soybean yields in relation to CT from the 7th year of the experiment onwards, especially under crop rotation and in growing seasons with lower water availability expressed by lower WRSI values. The percentage of NT soybean yield advantage over CT increased consistently over the time, and this increase was greater in CR than in CS, reaching on average 23%. The yields of wheat and maize were not influenced by the tillage systems, but the wheat yields were increased by crop rotation. In the most of the growing seasons, the soil chiseling, at every three years, did not increase significantly the yields of soybean, maize and wheat. Crop rotation and NT, allowed high and stable crop yields, especially under water-stress conditions. Results indicate the need of minimizing soil disturbance and diversifying cropping system for sustainable grain production in southern Brazil.

Assessment of water requirement of tobacco at Rajamundry (Andhra Pradesh)

Water use, Water Use Efficiency (WUE) and Water Requirement Satisfaction Index (WRSI) oftobacco varieties grown during rabi 1979 to 1988 at Rajamundry had been studied. The yield of tobacco was linearly andsignificantly correlated with amount of rainfall, water use and WRSI. The total amount of rainfall during growing seasonwas inadequate to meet the crop water requirements and these were partially met from stored soil moisture from previouskharif season. The excess rain during ripening stage of tobacco adversely affected the leaf yield and quality.The amount of water consumed varied between 110.0 to 186.6 mm for CTRI Special, 86.8 to 184.0 mm forJayashri. The mean WUE was found to be 6.1 and 6.4 kg/ha/mm respectively for CTRI Special and Jayashri. Themaximum amount of water consumed was 81.2 mm (i.e., 58.7%) during grand growth stage, followed by 36.5 mm(26.5%) during establishment stage and comparatively less (20.6mm) during maturity stage (14.8%). The average Kcvalue was maximum (0.5) during grand growth stage. WRSI showed decreasing trend from sowing towards maturity andthe rate of decrease was high in grand growth stage due to peak water consumption and less rainfall.

Analysis of NDVI time series using cross-correlation and forecasting methods for monitoring sugarcane fields in Brazil

Brazil is the largest sugarcane producer in the world and has a privileged position to attend to national and international marketplaces. To maintain the high production of sugarcane, it is fundamental to improve the forecasting models of crop seasons through the use of alternative technologies, such as remote sensing. Thus, the main purpose of this article is to assess the results of two different statistical forecasting methods applied to an agroclimatic index (the water requirement satisfaction index; WRSI) and the sugarcane spectral response (normalized difference vegetation index; NDVI) registered on National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (NOAA-AVHRR) satellite images. We also evaluated the cross-correlation between these two indexes. According to the results obtained, there are meaningful correlations between NDVI and WRSI with time lags. Additionally, the adjusted model for NDVI presented more accurate results than the forecasting models for WRSI. Finally, the analyses indicate that NDVI is more predictable due to its seasonality and the WRSI values are more variable making it difficult to forecast.

Evaluation of NASA satellite and modelled temperature data for simulating maize water requirement satisfaction index in the Free State Province of South Africa

Low density of weather stations and high percentages of missing values of the archived climate data in most places around the world makes it difficult for decision-makers to make meaningful conclusions in natural resource management. In this study, the use of NASA modelled and satellite-derived data was compared with measured minimum and maximum temperatures at selected climate stations in the Free State Province of South Africa. The NASA temperature data-fed Hargreaves evapotranspiration estimate was compared with the Penman–Monteith estimate to obtain regional coefficients for the Free State. The maize water requirement satisfaction index (WRSI) obtained using the NASA temperature data and calibrated Hargreaves equation was evaluated against the WRSI obtained using Penman–Monteith estimate. The data used is mostly from 1999 to 2008. The results of the comparison between measured minimum temperatures and NASA minimum temperatures show overestimation of the NASA values by between a monthly mean of 1.4°C and 4.1°C. NASA maximum temperatures seem to underestimate measured temperatures by monthly values ranging from 2.2 to 3.8°C. NASA-fed Hargreaves equation in its original form underestimates Penman–Monteith evapotranspiration by between 20% and 40% and hence its coefficient was calibrated accordingly. The comparison of the maize WRSI simulated with NASA temperatures showed a good correlation and small deviations from WRSI calculated from measured data. Thus, the use of NASA satellite and modelled data is recommended in the Free State Province in places where there are no meteorological readings, with special consideration of the biasness of the data.

Climatic risk zoning for corn and palisade grass (Brachiaria brizantha cv: Marandu) cultivated in integrated crop-livestock systems in São Paulo state, Brazil

Climatic risk zoning allows the identification of areas of low risk of reduced crop productivity due to climatic events. In Brazil, losses to agriculture due to climate are mainly caused by drought. The objective of this research was to determine areas of low climatic risk for corn and palisade grass cultivated in integrated crop-livestock systems in Sao Paulo state. Corn varieties characterized by a 120-day growing cycle and soil with three different water holding capacities (sandy, medium and clayey soils) were considered. A daily water balance model was used to simulate planting dates between September and December. The water requirement satisfaction index (WRSI) was calculated for critical phenological phases of both cultures (germination, emergence and tillering of palisade grass and flowering and grain filling of corn). The WRSI values, calculated for a minimum frequency of 80%, were located spatially using the SPRING v. 5.1 geographic information system and the most favorable periods for sowing in different areas were determined. The results showed that there are areas of low climatic risk for cultivation of corn and palisade grass in integrated crop-livestock production systems in Sao Paulo state. Although climatic risk in these areas also depends on soil type, the most favorable period for planting is between October and November.

Assessment of agricultural drought using a simple water balance model in the Free State Province of South Africa

Water Requirement Satisfaction Index (WRSI) at three different probability levels (20%, 50%, and 80%) was used to quantify drought affecting rain-fed maize production in the Free State Province of South Africa based on climate data from 227 weather stations. Results showed high spatial variability in the suitability of different areas: the southern and southwestern localities are unsuitable due to high drought incidences; the northern, central, and western regions are marginally suitable; the eastern, northerneastern areas and a few patches in the northwest are highly suitable with relatively low drought severity. Proper choice of maize varieties to suit conditions at different localities is crucial. The Mann–Kendall test and coefficient of variation were further used to determine trends and temporal variability, respectively, in the WRSI, seasonal rainfall, and seasonal maize water requirements. Results of this analysis revealed no significant positive trends in the WRSI, no significant negative trends in seasonal rainfall, and no significant positive trends in maize water requirements, contradicting previous findings of increased drought severity. Seasonal rainfall and the WRSI showed high interseasonal variability, while seasonal maize water requirements showed low variability. In view of these observations, it is apparent that realignment of management practices is an overdue prerequisite for sustainable maize production.

Developing an operational rangeland water requirement satisfaction index*

Developing an operational water requirement satisfaction index (WRSI) for rangeland monitoring is an important goal of the famine early warning systems network. An operational WRSI has been developed for crop monitoring, but until recently a comparable WRSI for rangeland was not successful because of the extremely poor performance of the index when based on published crop coefficients (K c) for rangelands. To improve the rangeland WRSI, we developed a simple calibration technique that adjusts the K c values for rangeland monitoring using long-term rainfall distribution and reference evapotranspiration data. The premise for adjusting the K c values is based on the assumption that a viable rangeland should exhibit above-average WRSI (values >80%) during a normal year. The normal year was represented by a median dekadal rainfall distribution (satellite rainfall estimate from 1996 to 2006). Similarly, a long-term average for potential evapotranspiration was used as input to the famine early warning systems network WRSI model in combination with soil-water-holding capacity data. A dekadal rangeland WRSI has been operational for east and west Africa since 2005. User feedback has been encouraging, especially with regard to the end-of-season WRSI anomaly products that compare the index's performance to ‘normal’ years. Currently, rangeland WRSI products are generated on a dekadal basis and posted for free distribution on the US Geological Survey early warning website at http://earlywarning.usgs.gov/adds/

Maize yield forecasting for Zimbabwe farming sectors using satellite rainfall estimates

Southern Africa rainfall station network is suffering from an unfortunate serious decline while climate-related food insecurity is worsening. In the current work, we demonstrate the possibility of exploiting the complementary roles that remote sensing, modeling, and geospatial data analysis can play in forecasting maize yield using data for the growing seasons from 1996/1997 to 2003/2004. Satellite-derived point-specific rainfall estimates were input into a crop water balance model to calculate the Water Requirement Satisfaction Index (WRSI). When these WRSI values were regressed with historical yield data, the results showed that relatively high skill yield forecasts can be made even when the crops are at their early stages of growth and in areas with sparse or without any ground rainfall measurements. Inferences about the yield at national level and small-scale commercial farming sector (SSCF) sector can be made at confidence levels above 99% from the second dekad of February. However, the most unstable models are those for the communal farming sectors whose inferences for yield forecast can only be made above the 95% confidence level from the end of February, after having recovered from a state of complete breakdown two dekads earlier. The large-scale commercial farming (LSCF) sector has generally the weakest fitting, but it is usable from the first dekad of February to the end of the rainy season. Validation of the national yield models using independent data set shows that an early estimation of maize yield is quite feasible by the use of the WRSI.