Thornthwaite Method Research Articles

Characterizing present and future drought changes over eastern China

ABSTRACTThis study aimed to characterize present and future drought changes over eastern China using observations and Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations. We used the standardized precipitation evapotranspiration index (SPEI) to characterize droughts at the timescales of 3‐ and 12‐month. We distinguished the spatial patterns of drought regimes (DRs) using the rotated empirical orthogonal function (EOF) on the SPEI. Our results identified three DRs centered in northern China (DR1), northeastern China (DR2), and southern China (DR3). Droughts in these regimes have increased in recent decades. Most CMIP5 models reproduce at least two of the DRs. The rotated EOF results indicate that the three DRs can jointly explain 46–68% of the SPEI variance (compared with approximately 60% in the observations). Among the 33 CMIP5 models analysed in this study, 13 simulated all three DRs well and showed a strong correlation pattern (>0.5). Further analysis indicated that both the external natural and greenhouse gas forcing experiments in CMIP5 reproduced the DRs, implying that natural variability and anthropogenic activity play important roles in the formation of these DRs. With continued climate warming, the three DRs over eastern China will persist. Despite the uncertainties in drought changes that mainly depend on the potential evapotranspiration methods, climate model results suggest that droughts would be aggravated under warming scenarios. The probability of severe droughts increase by the end of the century: 33% in DR1, 25% in DR2, 34% in DR3 in RCP4.5 and almost double in RCP8.5 scenario in Thornthwaite method based SPEI estimates.

Climate Characteristics of Safranbolu (Karabuk) and Saffron Cultivation

Saffron (Crocus sativus) has been one of the most important spices in the world since ancient times. Though there is a variety of information about its origin, it is believed to have emerged in Iran, Turkey, or Greece and have spread across the world. Saffron, which is commonly produced in the Mediterranean and Southwest Asian countries, is used in many different fields such as painting, medicine, perfumery, and food. Climate and soil conditions also play an important role in saffron production. Saffron, which shows a flexible characteristic in terms of temperature demand, shows resistance to cold temperatures down to -18 degrees and to summer temperatures up to 45 degrees. The type of soil suggested for the development of the plant is clay loam soil. Although saffron growing in Turkey has lost its former significance today, it is still carried out on a small scale in Safranbolu city. This study intends to show the positive effects of climatic elements prevailing in the region on the production of saffron, the world's most expensive plant, and to reestablish its former importance in the region. The climate data used in the present study were taken from the General Directorate of Meteorology of Turkey. The climatic conditions required by the Thornthwaite climate classification method. Systematic approach was used as a research method. The maps used in the study were prepared on ArcGIS 10.3 GIS (Geography Information System) package. According to the Thornthwaite method, Safranbolu is arid-low humidity in terms of rainfall activity, has a 2nd level mesothermal climate, has no water excess, and is closed to sea effect. Considering the climate demands of saffron, it can be said that the climate of Safranbolu city is suitable for saffron growing. In Safranbolu, saffron plants are currently cultivated only in few villages. However, more effort should be made to enhance the production of saffron, which is as precious as gold.

Why Do Different Drought Indices Show Distinct Future Drought Risk Outcomes in the U.S. Great Plains?

Vigorous discussions and disagreements about the future changes in drought intensity in the U.S. Great Plains have been taking place recently within the literature. These discussions have involved widely varying estimates based on drought indices and model-based projections of the future. To investigate and understand the causes for such a disparity between these previous estimates, the authors analyzed the soil moisture at the near-surface soil layer and the entire soil column, as well as the Palmer drought severity index, the Palmer Z index, and the standardized precipitation and evaporation index using the output from the Community Climate System Model, version 4 (CCSM4), and 25 state-of-the-art climate models. These drought indices were computed using potential evapotranspiration estimated by the physically based Penman–Monteith method (PE_pm) and the empirically based Thornthwaite method (PE_th). The results showed that the short-term drought indices are similar to modeled surface soil moisture and show a small but consistent drying trend in the future. The long-term drought indices and the total column soil moisture, however, are consistent in projecting more intense future drought. When normalized, the drought indices with PE_th all show unprecedented future drying, while the drought indices with PE_pm show comparable dryness with the modeled soil moisture. Additionally, the drought indices with PE_pm are closely related to soil moisture during both the twentieth and twenty-first centuries. Overall, the drought indices with PE_pm, as well as the modeled total column soil moisture, suggest a widespread and very significant drying in the Great Plains toward the end of the century. The results suggest that the sharp contrasts about future drought risk in the Great Plains discussed in previous studies are caused by 1) comparing the projected changes in short-term droughts with that of the long-term droughts and/or 2) computing the atmospheric evaporative demand using an empirically based method (e.g., PE_th). The analysis here may be applied for drought projections in other regions across the globe.

Regional Climate Change and Drainage Systems: Effects on Corn Productivity and Profitability in Campinas, Brazil

Abstract. Many natural systems are being affected by regional climate change. Regional climate change may affect the profitability and productivity of corn, which may require changes in the optimum design of drainage systems in the future. Our aim is to determine the effects of regional climate change on the relationship between drain spacing, corn productivity, and profitability and to derive estimates of productivity and profitability until the year 2100 using different future scenarios of climate simulation (CNTRL, HIGH, LOW, and MIDI). Our goal is to optimize drainage system designs that account for changes in climate using different drain spacing and types of soil in Campinas, Brazil. This study also evaluates the performance of the Eta regional climate model to simulate precipitation and air temperature for the study area. Evapotranspiration calculated with the Thornthwaite method (using observed and simulated data) and precipitation data were used as input for the SISDRENA model, which evaluates the performance of one-dimensional drainage systems. As output, the SISDRENA model provides information about drainage system design and indexes of water stress, productivity, and profitability. The general conclusion is that the Eta model is a good tool for studying the effects of climate change in the region because the simulations approximated the observed data. All sets of analyzed years indicated that a spacing of 20 m between drains was best, producing the highest average productivity and profitability. Clay loam soils tended to have higher productivity and profitability than clay soils, which translates to greater profit for the producer. However, the temperature and precipitation variations predicted by the Eta model showed that corn profitability may be reduced, changing the potential productivity in Campinas, Brazil.

ASSESSING GLOBAL CLIMATE VARIABILITY UNDER COLDEST AND WARMEST PERIODS AT DIFFERENT LATITUDINAL REGIONS

Effect of climate change on water balance will play a key role in the biosphere system. To study the global climate change impact on water balance during 95-year period (1901-1995), long-term grid climatic data including global mean monthly temperature and precipitation at 0.5 x 0.5 degree resolution were analysed. The trend and variation of climate change, the time series of monthly air temperature and precipitation data were aggregated into annual arithmetic means for two extreme periods (1901-1920 and 1990-1995). The potential evapotranspiration (Eo) was calculated using Thornthwaite method.<br />The changes in mean annual value were obtained by subtracting the maximum period data from 1990 to 1995 (Max) with the minimum period data from 1901 to 1920 (Min). The results revealed that over 95-year period, mean global air temperature increased by 0.57oC. The temperature increase varied greatly in Asia, with more than 3.0oC, especially at 45-70oN, as well over the northern part of America (60-65oN) and Europe (55- 75oN). In low latitude across Asia, Africa, and South America, the variation was less than 1.5oC. In 80-85ºN region, the variation was relatively small and at higher latitudes it increased<br />significantly. Precipitation varied temporally and spatially. In the 40-45ºN and 40-45ºS regions, increasing precipitation of more than 100 mm occurred during the June-August and<br />September-November, especially in the northern hemisphere. The Eo increase of 2000 mm during 95 years occurred in the tropical northern America, middle Africa, and South-East Asia. A grid in Central Java of Indonesia showed that the Eo increase of 2500 mm during 95 years resulted in the decrease of growing period by 100 days. In coping with climate change, adjustment of cropping calendar is imperative.

ASSESSING GLOBAL CLIMATE VARIABILITY UNDER COLDEST AND WARMEST PERIODS AT DIFFERENT LATITUDINAL REGIONS

Effect of climate change on water balance will play a key role in the biosphere system. To study the global climate change impact on water balance during 95-year period (1901-1995), long-term grid climatic data including global mean monthly temperature and precipitation at 0.5 x 0.5 degree resolution were analysed. The trend and variation of climate change, the time series of monthly air temperature and precipitation data were aggregated into annual arithmetic means for two extreme periods (1901-1920 and 1990-1995). The potential evapotranspiration (Eo) was calculated using Thornthwaite method.<br />The changes in mean annual value were obtained by subtracting the maximum period data from 1990 to 1995 (Max) with the minimum period data from 1901 to 1920 (Min). The results revealed that over 95-year period, mean global air temperature increased by 0.57oC. The temperature increase varied greatly in Asia, with more than 3.0oC, especially at 45-70oN, as well over the northern part of America (60-65oN) and Europe (55- 75oN). In low latitude across Asia, Africa, and South America, the variation was less than 1.5oC. In 80-85ºN region, the variation was relatively small and at higher latitudes it increased<br />significantly. Precipitation varied temporally and spatially. In the 40-45ºN and 40-45ºS regions, increasing precipitation of more than 100 mm occurred during the June-August and<br />September-November, especially in the northern hemisphere. The Eo increase of 2000 mm during 95 years occurred in the tropical northern America, middle Africa, and South-East Asia. A grid in Central Java of Indonesia showed that the Eo increase of 2500 mm during 95 years resulted in the decrease of growing period by 100 days. In coping with climate change, adjustment of cropping calendar is imperative.

Evaluation of Percolation Rate of Bedrock Aquifer in Coastal Area

Estimation of groundwater hydrologic cycle pattern is one of the most critical issues in sustainable management of groundwater resources in coastal area. This study estimated groundwater percolation by using the water balance methodology and hydrogeological characteristics of land use and soil. Evapotranspiration was computed by using the Thornthwaite method, and surface runoff was determined by using the SCS-CN technique. Groundwater storage change was obtained as 229 mm/a (17.8% of the average annual rainfall, 1286 mm/a), with 693 mm/a (60.1%) of evapotranspiration and 124 mm/a (9.6%) of surface runoff. Rainfall and groundwater storage change was highly correlated, comparing with the relationships between rainfall and evapotranspiration, and between rainfall and surface runoff. This result indicates that groundwater storage change responds more sensitively to precipitation than evapotranspiration and surface runoff.

How to compute the land cover evapotranspiration at regional scale? A spatial approach of Emilia-Romagna region

The Earth is rapidly changing in both its climate and its land distribution. The numerous methods from the literature show various possibilities to assess the crop evapotranspiration and evaporation rate, both with direct measurements and empirical formulas. The present paper brings forward a methodology that demonstrates how to compute the potential land cover evapotranspiration (ET c ) at regional scale using climate data from 13 meteorological stations, empirical equations, Corine Land Cover data, and the Geographical Information System (GIS). Based on Thornthwaite method and evapotranspiration coefficients, the study assesses the ET c of Emilia-Romagna region in four stages. Moreover, the Budyko approach was applied to calculate the actual evapotraspiration (AET 0 ) and actual land cover evapotranspiration (AET c ) to identify the critical areas of water deficit. Po Plain represents an area with high evapotranspiration rate, due to temperatures and cultivation patterns. A value of 778.87 mm/year at Ferrara station was calculated for the potential evapotranspiration (ET 0 ), while the ET c ranging to 800-1000 mm/year in the central and northeastern part of the region. The AET c reached the maximum values of724 mm in the southcentral part of the Emilia-Romagna

Functionally relevant climate variables for arid lands: a climatic water deficit approach for modelling desert shrub distributions

AbstractAimWe have three goals. (1) To develop a suite of functionally relevant climate variables for modelling vegetation distribution on arid and semi‐arid landscapes of the Great Basin, USA. (2) To compare the predictive power of vegetation distribution models based on mechanistically proximate factors (water deficit variables) and factors that are more mechanistically removed from a plant's use of water (precipitation). (3) To quantify the climate gradients that control shrub distributions in a cold desert environment.LocationThe central basin and range ecoregion of the western USA (36–42°N).MethodsWe used a modified Thornthwaite method to derive monthly water balance variables and to depict them using a water balance climograph. Eighteen variables were calculated from the climograph, representing different components of the seasonal water balance. These were used in boosted regression tree models to derive distribution models for 18 desert shrub species. The water balance approach was compared with an approach that used bioclimatic variables derived from the PRISM (Parameter‐elevation Relationships on Independent Slopes Model) climate data.ResultsThe water balance and bioclimatic approaches yielded models with similar performance in predicting the geographical distribution of most shrub species. Cumulative annual climatic water deficit was consistently the most important water balance variable for predicting shrub type distributions, although predictions were improved by the inclusion of variables that describe the seasonal distribution of water balance such as water supply in the spring, fall actual evapotranspiration, monsoonality and summer decline in actual evapotranspiration.Main conclusionsThe water balance and bioclimatic approaches to species distribution modelling both yielded similar prediction accuracies. However, the water balance approach offers advantages over the bioclimatic approach because it is mechanistically derived to approximate physical processes important for plant growth.

Improvement and adaptability evaluation of standardized precipitation evapotranspiration index

In view of the question about larger estimate error in arid areas by using the Thornthwaite method of estimating potential evaporation in the process of calculating standardized precipitation evapotranspiration index, we use the FAO Penman-Monteith method instead of Thornthwaite method to improve the method of calculating the standardized precipitation evapotranspiration index. Based on the 1961-2013 daily meteorological data offered by 541 stations of Meteorology Bureau, the distribution of test and standardized rainfall index, Palmer drought severity index and soil moisture are used to analyze the consistency with standardized rainfall evaporation index when used to evaluate drought in the applicability of area and season. Result shows that the improvement on the method of evaporation capacity calculation can significantly expand the application of standardized precipitation evapotranspiration index in area and season, making standardized precipitation evapotranspiration index applied to national drought assessment well, making up the shortcomings in the applicability of standardized precipitation evapotranspiration index in winter at a short time scale level in arid region. In addition, both yearly time scale and monthly time scale of drought assessment ability about modified standardized precipitation evapotranspiration index are improved, meeting the demand for drought assessment in our country, which is given priority to seasonal drought.

Determinação da evapotranspiração por diferentes métodos e sua aplicação no índice de seca na Campanha Gaúcha, Brasil

O desempenho dos métodos para estimar a evapotranspiração de referência (ETo) varia em função das condições climáticas locais. Por isso, este trabalho tem como objetivos: a) avaliar o desempenho dos métodos indiretos de cálculo da ETo, na escala diária e mensal, para o período de outubro a março; b) avaliar os métodos para uso em estudos de zoneamento vitícola no cálculo do Índice de Seca (IS); ambos tendo como método-padrão Penman-Monteith-FAO. Foram utilizados dados meteorológicos diários dos meses de outubro a março, de 1961 a 2010, dos postos meteorológicos da rede da FEPAGRO e do INMET, localizados na região da Campanha-RS. A ETo foi calculada pelos métodos de Thornthwaite, Camargo, Makkink, Radiação Solar, Jensen-Haise, Linacre, Hargreaves-Samani, Blaney-Criddle e Penman-Monteith, com posterior aplicação ao IS, comparando aos resultados obtidos no método-padrão. Verifica-se que, na ETo na escala diária, ocorrem diferenças quanto ao desempenho entre os métodos, variando a classificação de "sofrível" a "muito bom". Na escala mensal, os métodos têm o melhor desempenho, apresentam classificação como "bom", para os métodos de Radiação Solar, Makkink, Camargo e Blaney-Criddle. Para o IS, no mês de março, verificou-se que os métodos de Thornthwaite e Camargo apresentam desempenho "ótimo", sendo, portanto, metodologias recomendadas para a estimativa da ETo no Sistema de Classificação Climática Multicritério (CCM), para a Campanha-RS.

<b>Reference evapotranspiration models using different time scales in the Jaboticabal region of São Paulo, Brazil

The aim of this paper is to compare 18 reference evapotranspiration models to the standard Penman-Monteith model in the Jaboticabal, São Paulo, region for the following time scales: daily, 5-day, 15-day and seasonal. A total of 5 years of daily meteorological data was used for the following analyses: accuracy (mean absolute percentage error, Mape), precision (R2) and tendency (bias) (systematic error, SE). The results were also compared at the 95% probability level with Tukey’s test. The Priestley-Taylor (1972) method was the most accurate for all time scales, the Tanner-Pelton (1960) method was the most accurate in the winter, and the Thornthwaite (1948) method was the most accurate of the methods that only used temperature data in the equations.

VARIABILIDADE ESPAÇO TEMPORAL DA EVAPOTRANSPIRAÇÃO POTENCIAL NO SUBMÉDIO DO RIO SÃO FRANSCISCO UTILIZANDO A ANÁLISE FATORIAL EM COMPONENTES PRINCIPAIS

Evapotranspiration is one of the most important processes of the hydrological cycle, consisting of the link between energy, climate and water availability. Therefore the aim of this work was to apply multivariate statistics, factor analysis by principal components (PCA) in monthly series of potential evapotranspiration (ETP) in the Lower Basin of the Valley of the Sao Francisco region. We chose this region because it is embedded in the Brazilian semiarid region, which is one of the areas of the country more susceptible to the effects of climate change, both in the physical aspect as socioeconomic. The data used are time series (1960-1990) average air temperature (Tmed) expanding in grids with a resolution of 0.5 ° x 0.5 ° derived from the Regional Climates for Impacts Studies Providing ( PRECIS ) the Hadley Centre model. To determine the ETP was chosen the method of Thornthwaite and Mather (1955). Factor analysis was applied to the spatio-temporal mode for ETP data using SPSS software. The average value of 1.386 mm was observed for annual series of ETP in the study area. For the study period of 1960-1990 the set of analyzed data can be represented by three factors together explain 96.7 % of the variability of the data studied. The addition of ( 3.3% ) are associated with noise. The explanation of the first factor is directly influenced by variables related to water availability and energetic. The second factor can is associated with incidence of rainfall producing systems, such as Tropospheric Cyclonic Vortex and the ITCZ, and the influence of land use - irrigated crops . Finally the third and last factor has a direct relation to the change of dry to wet, and possibly soil type of the region.

Tracking Interannual Streamflow Variability with Drought Indices in the U.S. Pacific Northwest

Abstract Drought indices are often used for monitoring interannual variability in macroscale hydrology. However, the diversity of drought indices raises several issues: 1) which indices perform best and where; 2) does the incorporation of potential evapotranspiration (PET) in indices strengthen relationships, and how sensitive is the choice of PET methods to such results; 3) what additional value is added by using higher-spatial-resolution gridded climate layers; and 4) how have observed relationships changed through time. Standardized precipitation index, standardized precipitation evapotranspiration index (SPEI), Palmer drought severity index, and water balance runoff (WBR) model output were correlated to water-year runoff for 21 unregulated drainage basins in the Pacific Northwest of the United States. SPEI and WBR with time scales encompassing the primary precipitation season maximized the explained variance in water-year runoff in most basins. Slightly stronger correlations were found using PET estimates from the Penman–Monteith method over the Thornthwaite method, particularly for time periods that incorporated the spring and summer months in basins that receive appreciable precipitation during the growing season. Indices computed using high-resolution climate surfaces explained over 10% more variability than metrics derived from coarser-resolution datasets. Increased correlation in the latter half of the study period was partially attributable to increased streamflow variability in recent decades as well as to improved climate data quality across the interior mountain watersheds.

Water budget comparison of global climate models and experimental data in Onça Creek basin, Brazil

Abstract. Groundwater is an important part of the hydrological cycle, accounting for more than 25% of human needs on the global scale. As a result of aquifer overexploitation associated with climate change, even in the most conservative future climate scenarios, mean water-table levels can experience drastic drops. Although there are efforts to include groundwater dynamics in global climate models (GCMs), its influence is still not taken into full account in GCM water budgets, although it is as important as the other water sources considered. To assess the role of percolation in the water balance, we compared the water budget from climate forcing scenarios using 10 GCMs with the water budget from experimental data of a basin in São Paulo state, Brazil. We used the delta factor approach to correct the bias of the model's temperature and precipitation for a control period from 1970 to 1999, and calculated evapotranspiration using the Thornthwaite method. Experimental data for runoff and interception were derived for the basin’s representative crops (sugar cane and pasture) for both water budgets. As the GCMs ignore subsurface flow and the only input considered is precipitation and snow melt, the excess surface water is assumed to be redistributed among the other water budget components. The experimental data shows that there is enough available water for infiltration, indicating that recharge cannot be ignored in the water balance. This leads to the possibility of the models’ overestimating the other components to compensate for the ignored recharge.

Hydrological studies in experimental and representative basins in Pernambuco State, Brazil

Abstract. Hydrological studies in experimental and representative basins are of fundamental importance for water resources management. This paper presents some activities of hydrological research in experimental and representative basins of the State of Pernambuco, Brazil. The study areas are located at Tapacurá and Mundaú representative basins and at the Gameleira experimental basin, and in experimental plots in Pajeú basin. In the Tapacurá basin, three studies were performed: (1) different monthly coefficients "k" of the Thornthwaite method were tested to calculate the effective temperature and, consequently, the reference evapotranspiration, giving rise to the method identified as Modified Thornthwaite; (2) the spatial variability of the retention curve and hydraulic conductivity parameters were analysed using the Beerkan method; (3) changes in vegetation cover were evaluated through the NDVI and NDWI indexes using TM–Landsat 5 images. In the Mundaú representative basin, the performance of different evapotranspiration methods was evaluated and compared to the FAO standard method, Penman-Monteith. In the Pajeú basin, the experimental plot is covered by pasture and sensors were installed to monitor the following variables: rainfall, air temperature, the energy balance components (net radiation, latent and sensible heat, and soil heat flux), wind velocity and CO2 flux into atmosphere, soil moisture and runoff.

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.

Temperature-based approaches for estimating monthly reference evapotranspiration based on MODIS data over North China

Reference evapotranspiration (ETo) maps play an important role in distributed hydrological modeling and are particularly useful for regional agricultural and water resource management. In the Three-North Shelter Forest Program, water requirements (i.e., ETo) of different land use types are important preconditions for afforestation program management. The Food and Agriculture Organization Penman–Monteith (FAO-PM) method is the most common method for estimating ETo, but it requires many different types of meteorological data, and few stations with adequate meteorological resources exist in the Three-North regions. In addition, the spatial distribution of ordinary meteorological stations is limited. This study employed two temperature-based ETo methods, Hargreaves and Thornthwaite. The monthly mean, maximum, and minimum air temperatures were estimated using moderate resolution imaging spectroradiometer (MODIS) data. The original coefficients of Hargreaves and mean temperatures of Thornthwaite were modified for regional calibration (with the FAO-PM method as the standard). In the comparison between the original/adjusted Hargreaves and the original/adjusted Thornthwaite methods, the adjusted Hargreaves method was appropriate for estimating ETo in the Three-North regions. The average mean bias error (MBE) was −0.21 mm, the relatively root mean square error (RRMSE) was 13.44 %, the correlation coefficient (R 2) was 0.85, and the slope (b) was 1.00 for the monthly ETo. While the MBE was 2.32 mm, the RRMSE was 7.07 %, the R 2 was 0.90, and the b was 1.00 for the annual ETo. Therefore, it is possible to estimate monthly and annual ETo values for other parts of the country or the world using adjusted Hargreaves with the estimated air temperature data instead of using the FAO-PM with observed data.

Dias trabalháveis para o manejo do solo em função da chuva e da disponibilidade hídrica do solo em diferentes regiões brasileiras

The use of machinery in agriculture is increasing. This leads to soil compaction or degradation when the machinery is operated under inappropriate soil conditions, which in turn results in decreasing crop yields. Therefore, the aim of this study was to identify the periods of the year when it is appropriate to use machinery for soil management, as a function of rainfall and soil moisture, in traditional agricultural regions in southern Brazil. The study used daily rainfall and air temperature data from Piracicaba, SP, Passo Fundo, RS, Londrina, PR and Dourados, MS, Brazil. Favorable conditions were calculated considering daily rainfall lower than 5 mm and soil moisture between 40 and 90% of soil water holding capacity. Daily soil water balance was calculated by the Thornthwaite and Mather (1955) method, for a soil water holding capacity of 100 mm, which represents the main soils of the studied regions. The Markov chain was applied and used to calculate the conditional probabilities which were used for estimating the sequential working days in each ten-day period throughout the year. The working days technique is an important tool for determining the most appropriate periods of the year for soil management. The annual rainfall and soil moisture variability was used to identify the periods of the year with low, medium and high suitability for soil management. For the assessed locations, there was a predominance of 11 to 20 working days per month, except for Londrina where up to 10 working days per month predominated.

Improvement to the Thornthwaite Method to Study the Runoff at a Basin Scale Using Temporal Remote Sensing Data

Most of the popular hydrological models are intensive data driven hence, it has become a constraint in computing runoff of river basins where the meteorological data availability is scant. Studying environmental impact assessment on runoff has also become complex in many basins due to non-availability of sufficient historic meteorological data. Directly or indirectly, major components of hydrological cycle such as evapotranspiration and soil moisture are dependent on land use pattern at basin scale. Keeping in view of this, in this paper, an attempt was made to propose modification to simple monthly water balance model by integrating potential evapotranspiration with land use coefficients that were derived from the temporal satellite remote sensing data to compute runoff at basin scale. Godavari Basin, India was selected as study basin to demonstrate the approach. Monthly land use coefficients of all land use classes were computed during the calibration process of the model by matching the computed runoff with field runoff. Runoff during the last 18 years (1990–91 to 2007–08) was computed using the developed methodology. Four years datasets were used for model calibration and the rest of the data for model validation. Spatial annual groundwater flux, reservoir flux and domestic water consumption grids were computed using the field data and integrated with the model in computing runoff. From the Nash-Sutcliffe efficiency coefficient, it is found that computed runoff is very well matching the field runoff. The demonstrated approach is found to be more accurate and simple in computing runoff at basin scale in absence of high intensity meteorological data.