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The semiarid lands of Northeast Brazil represent one of the most densely populated regions of the country. Rainfall variability together with land degradation and large‐scale poverty in rural areas makes this region vulnerable to droughts. Most of the agriculture in this region is rainfed and deficient rainfall leads to severe drought impacts. In this review, we examine different short‐ and long‐term strategies directed to cope with possible impacts of droughts proposed by the government, farmers, civil society, and the private sector. These are approaches to adaptation to drought in the Northeast of Brazil, and among them, we have agricultural management and soil conservation and better management of water resources. Other actions include seasonal climate forecasts and funds transfer and credits to affected small‐scale farmers. Although some of these actions are for the short term and may help to survive the drought situation, they may be only postdisaster mitigation options that do not improve adaptive capacity. They favor maladaptation and create dependency of farmers to government actions. Some experiences such as AdaptaSertão show potential benefits for small‐scale farmers. We identify key challenges for moving toward a more holistic risk management approach and highlight the need to integrate actions and tools for adaptation, combining technology‐based solutions with in‐depth knowledge of local and regional social, economic, and cultural aspects, among them seasonal climate forecasts and drought impacts studies, among some other proactive predisaster ways, rather than reactive postdisaster actions. Adaptation strategies must increase long‐term resilience of food production in the Brazilian Northeast, going beyond an individual drought event. The semiarid lands of Northeast Brazil NEB represent one of the most densely populated regions of the country. Rainfall variability together with land degradation and large‐scale poverty in rural areas make this region vulnerable to droughts in the present. Approaches to adaptation to drought in the NEB vary from agricultural practices and credits to farmers to infrastructure and climate forecasts. Adaptation strategies must increase long‐term resilience of food production in the Brazilian Northeast, going beyond an individual drought event.

This study evaluated the effects of climate change on sugarcane yield, water use efficiency, and irrigation needs in southern Brazil, based on downscaled outputs of two general circulation models (PRECIS and CSIRO) and a sugarcane growth model. For three harvest cycles every year, the DSSAT/CANEGRO model was used to simulate the baseline and four future climate scenarios for stalk yield for the 2050s. The model was calibrated for the main cultivar currently grown in Brazil based on five field experiments under several soil and climate conditions. The sensitivity of simulated stalk fresh mass (SFM) to air temperature, CO2 concentration [CO2] and rainfall was also analyzed. Simulated SFM responses to [CO2], air temperature and rainfall variations were consistent with the literature. There were increases in simulated SFM and water usage efficiency (WUE) for all scenarios. On average, for the current sugarcane area in the State of São Paulo, SFM would increase 24 % and WUE 34 % for rainfed sugarcane. The WUE rise is relevant because of the current concern about water supply in southern Brazil. Considering the current technological improvement rate, projected yields for 2050 ranged from 96 to 129 t ha−1, which are respectively 15 and 59 % higher than the current state average yield.

The consumptive use of water by irrigated crops is typically quantified using the crop coefficient–reference evapotranspiration (Kc–ETo) procedure; yet, recent results showed that Kc might change with ETo, in response to high atmospheric demand. It is not known if the reduced Kc at high ETo applies to other crops with different aerodynamic features of the canopies. This paper seeks to provide the Kc values for soybean, wheat and potato, and propose an adaptation to the Kc–ETo procedure, hypothesising that the inverse relation between Kc and ETo would be general for all types of crops. Our results showed average Kc values of 0.90, 1.18 and 1.28, respectively, for soybean, wheat and potato cropping systems in the Brazilian cropping systems. However, Kc decreased as ETo increased, for all crops considered in this study, because of the increase of internal plant resistances to vapour diffusion from the leaves to the atmosphere. When ETo was above > 4 mm d−1, the water use by such crops was lower than that prescribed by Allen et al. (JAMA, 1998). The time-based Kc curves in Allen et al. (JAMA, 1998) are inappropriate for the studied crops under high demanding conditions and, besides the considerations suggested by Allen et al. (JAMA, 1998) (i.e., crop development stage, presence or absence of weeds), Kc recommendations for practical irrigation management should be based on the average ETo values of the previous days of the irrigation procedure.

Bioenergy from sugarcane production is considered a key mitigation strategy for global warming. Improving its representation in land surface models is important to further understand the interactions between climate and bioenergy production, supporting accurate climate projections and decision‐making. This study aimed to calibrate and evaluate the Joint UK Land Environment Simulator (JULES) for climate impact assessments in sugarcane. A dataset composed of soil moisture, water and carbon fluxes and biomass measurements from field experiments across Brazil was used to calibrate and evaluate JULES‐crop and JULES‐BE parametrizations. The ability to predict the spatiotemporal variability of sugarcane yields and the impact of climate change was also tested at five Brazilian microregions. Parameters related to sugarcane allometry, crop growth and development were derived and tested for JULES‐crop and JULES‐BE, together with the response to atmospheric carbon dioxide, temperature and low‐water availability (CTW‐response). Both parametrizations showed comparable performance to other sugarcane dynamic models, with a root mean squared error of 6.75 and 6.05 t ha−1 for stalk dry matter for JULES‐crop and JULES‐BE, respectively. The parametrizations were also able to replicate the average yield patterns observed in the five microregions over 30 years when the yield gap factors were taken into account, with the correlation (r) between simulated and observed interannual variability of yields ranging from 0.33 to 0.56. An overall small positive trend was found in future yield projections of sugarcane using the new calibrations, with exception of the Jataí mesoregion which showed a clear negative trend for the SSP5 scenario from the years 2070 to 2100. Our simulations showed that an abrupt negative impact on sugarcane yields is expected if daytime temperatures above 35°C become more frequent. The newly calibrated version of JULES can be applied regionally and globally to help understand the interactions between climate and bioenergy production. In this study, we aimed to calibrate and evaluate the Joint UK Land Environment Simulator (JULES) for climate impact assessments in sugarcane. Parameters related to sugarcane allometry, crop growth and development were derived and tested for the model, together with the crop response to atmospheric carbon dioxide, temperature and drought (CTW‐response). The model showed good agreement against highly monitored experiments and represented spatiotemporal pattern of sugarcane production across five Brazilian regions. We found an overall small positive trend in future yield projections for sugarcane, but an abrupt negative impact is expected if daytime temperatures above 35°C become more frequent.

This study compares the performance of Global Ensemble Forecast System (GEFS) and European Centre for Medium-Range Weather Forecasts (ECMWF) precipitation ensemble forecasts in Brazil and evaluates different analog-based methods and a logistic regression method for postprocessing the GEFS forecasts. The numerical weather prediction (NWP) forecasts were evaluated against the Physical Science Division South America Daily Gridded Precipitation dataset using both deterministic and probabilistic forecasting evaluation metrics. The results show that the ensemble precipitation forecasts performed commonly well in the east and poorly in the northwest of Brazil, independent of the models and the postprocessing methods. While the raw ECMWF forecasts performed better than the raw GEFS forecasts, analog-based GEFS forecasts were more skillful and reliable than both raw ECMWF and GEFS forecasts. The choice of a specific postprocessing strategy had less impact on the performance than the postprocessing itself. Nonetheless, forecasts produced with different analog-based postprocessing strategies were significantly different and were more skillful and as reliable and sharp as forecasts produced with the logistic regression method. The approach considering the logarithm of current and past reforecasts as the measure of closeness between analogs was identified as the best strategy. The results also indicate that the postprocessing using analog methods with long-term reforecast archive improved raw GEFS precipitation forecasting skill more than using logistic regression with short-term reforecast archive. In particular, the postprocessing dramatically improves the GEFS precipitation forecasts when the forecasting skill is low or below zero.

Conflicts over water use and the high demand for food and biofuels have motivated the use of wastewater in irrigated agriculture. The study aimed to evaluate the nitrogen losses through nitrate leaching and nitrous oxide emission for sugarcane first ratoon irrigated by subsurface drip (SDI) with fresh water and treated domestic sewage (TDS) and traditional crop management under rainfed conditions. Therefore, the following treatments were implemented: T1—non-irrigated and topdressing fertilization; T2—irrigated with TDS, with fertigation; T3—irrigated with TDS, without fertigation; T4—irrigated with fresh water, with fertigation; T5—irrigated with fresh water, without fertigation. The nitrogen ( N ) fertilizer applied corresponded to 120 kg ha −1 to all treatments, with broadcast fertilization for nonirrigated cropping and, for the irrigated plots, it was performed by supplementing the concentration of the nutrients in the TDS and freshwater. All the fertigated treatments had lower leaching losses than nonirrigated treatment with topdressing fertilization, the total N loss for nonirrigated plots differed significantly from irrigated treatments, with a total loss of 16.36 kg N ha −1 . The application of TDS by SDI to meet the needs for water and nutrients resulted in a decrease of N losses by NO 3 − leaching and N 2 O emissions, compared with traditional sugarcane cultivation under non-irrigated with topdressing fertilization (total of 16.36 kg ha −1 for T1), being the nitrate leaching the main factor that contributed to the N loss with a loss of 71% for T1 (11.50 kg ha −1 ). Irrigation with TDS, in addition to providing nutrients and water for sugarcane cultivation, can help minimize nitrogen contamination compared to conventional management methods through SDI systems.

Due to the lack of basic information on water required by maize (Zea mays L.) in Brazil, the large amount of water applied usually exceeds crop requirements, wasting water and energy. In this study, we measured crop evapotranspiration (ETc) as evaporative heat flux from a centre pivot-irrigated maize plantation in Southern Brazil during winter and summer seasons, using the Bowen ratio method to evaluate how the degree of canopy-atmosphere coupling affects crop water needs and irrigation management. Irrigation requirements were determined by comparing ETc with reference evapotranspiration (ETo), derived from the Penman–Monteith equation and expressed as the ETc/ETo (Kc) ratio. In this study, the average Kc values obtained were 1.31 and 0.90 for the winter and summer, respectively. Using aerodynamic and canopy resistance measurements, the decoupling factor (Ω) was computed. Ω values tending to zero (0.09 and 0.20 for winter and summer, respectively) showed that strong coupling of maize plants to the atmosphere and sensitivity to high air temperatures, vapour pressure deficits and wind speed caused variations in Kc in relation to ETo ranges. During the experimental period, the Kc value ranged from 0.92 when the ETo exceeded 4 mm d−1 to 1.64 when the ETo was less than 2 mm d−1.

This article assesses sugarcane yield gaps (YG) in Brazil to determine the degree to which production can be increased without land expansion. In our scenario assessments, we evaluated how much of the projected sugarcane demand to 2024 (for both sugar and bioethanol) can be satisfied through YG closure. The current national average yield is 62% of yield potential estimated for rainfed conditions (i.e., a YG of 38%). Continuing the historical rate of yield gain is not sufficient to meet the projected demand without an area expansion by 5% and 45% for low- and high-demand scenarios, respectively. Closing the exploitable YG to 80% of potential yield would meet future sugarcane demand, with an 18% reduction in sugarcane area for the low-demand scenario or a 13% expansion for the high-demand scenario. A focus on accelerating yield gains to close current exploitable YG is a high priority for meeting future demand while minimizing pressure on additional land requirements.

In some of the traditional areas growing sugarcane and in most of the expanding regions in Brazil, water deficit stress is a limiting factor and irrigation is usually needed to assure economically viable sugarcane yields. This research evaluated the water requirements of a drip-irrigated second ratoon sugarcane crop based on three different spatial scales: field, plant and leaf. The Bowen ratio method (BRM) was used to evaluate the mass and energy exchanges over the field, further computing the crop evapotranspiration (ETc). Sap flow by heat balance method installed in four representative stalks was used to evaluate the water use at the plant scale, and an infra-red gas analyser was used to evaluate leaf transpiration and stomatal conductance at the leaf scale. Comparing ETc and reference evapotranspiration we found that the crop coefficients for dry and wet seasons were 0.81 and 0.98, respectively. Evapotranspiration peaks of 7 mm day −1 were observed under conditions of strong crop-atmosphere coupling and high net radiation values. The stomatal conductance ranged from 0.09 to 0.19 mmol m −2  s −1 in dry and wet seasons respectively, showing sensitivity to the atmospheric conditions, notably the vapour deficit pressure and wind speed. BRM ranged from 3.7 to 4.4 mm day −1 and leaf transpiration ranged among 3.4 and 4.2 mm day −1 . In an irrigated sugarcane production area in Brazil, water consumption of the sugarcane crop was highly correlated with atmospheric conditions.

Crop irrigation requirements are usually estimated based on crop evapotranspiration (ETc) as determined by the reference evapotranspiration (ETo) and crop coefficient (Kc). There is a lack of knowledge on the irrigation requirements of tropical forage crops in Brazil, contrasting with the increasing use of irrigation in pastures. The effort of this study was to investigate what would be the water needs of tropical forages in Southern Brazil, based on a robust experimental database. The study was carried out in São Paulo State-Brazil using different forages species and their combinations [Guinea grass (GG); Guinea grass + black oat + ryegrass (GOR); Bermuda grass (BG), and Bermuda + black oat + ryegrass (BOR)]. The experimental fields were fully irrigated, and the Kc values were derived from ETc measurements on lysimeters; ETo was estimated using daily data from a nearby weather station and the standard FAO56 parameterization. Mean daily ETc values for GG, GOR, BG and BOR were 4.1, 2.9, 3.6, and 3.4 mm, respectively, and respective mean Kc values were 0.99, 0.90, 1.0, and 0.94. Average Kc values for all plots decreased as ETo increased, producing a negative Kc-ETo relationship, mainly when ETo reached values greater than 5 mm d−1. This was most likely due to internal plant stomatal resistance to vapor release from the leaves diffusing to the atmosphere at high ETo. So, the time-based Kc curves described by FAO 56 manual should be adjusted for the analyzed crops considering different ranges of ETo to improve the required irrigation depth.