Automation of hydrological drought typology to study drought propagation in a tropical catchment

Understanding how droughts propagate through the hydrological cycle from precipitation to streamflow and groundwater is important for improving water and risk management policies. At the catchment scale, the analysis of drought propagation and classification into drought types is usually done manually, which can be time consuming and difficult to replicate. Here, we developed an automated, objective procedure for classification of different drought types with the aim to study drought propagation in the tropics. The method was applied to the Savegre catchment in Costa Rica as a proof-of-concept. We first confirmed that drought events in the catchment could be classified into the process-based typology from the literature: classical rainfall deficit drought, wet-to-dry season drought, and composite drought. The automation algorithm was able to replicate the classification obtained with the manual typology with the exception of two events, and thus it is a development towards objective and time efficient hydrological drought analysis in tropical catchments. Most of the detected hydrological droughts (80% and 76% of all river discharge and baseflow droughts, respectively) were classical rainfall deficit droughts, which suggests that climate plays a more important role in drought development than catchment characteristics in this catchment. However, the importance of catchment characteristics was revealed by the presence of severe composite drought events and by the attenuation of significant precipitation droughts.

Timing of nitrogen application and cover crops on upland rice economic viability

The objective of this work was to evaluate the economic viability and competitiveness of upland rice (Oryza sativa), compared with flooded rice, in a system with different nitrogen fertilization timing and cover crops in Southeastern Brazil. The treatments consisted of upland rice grown under Urochloa brizantha or Urochloa ruziziensis straw, with the following fertilization: T, 30 kg ha-1 N at rice sowing + no extra N supply (0 kg ha-1); C, 30 kg ha-1 N at rice sowing + 90 kg ha-1 N at rice tillering; A2, 30 kg ha-1 N at rice sowing + 90 kg ha-1 N one day before rice sowing; and A1, 30 kg ha-1 N at rice sowing + 90 kg ha-1 N in the living cover crops. Total operating cost, gross revenue, operating profit, profitability index, and equilibrium price were determined. Upland rice results in a monetary gain for the farmer similar to that of flooded rice when nitrogen is added, regardless of fertilization timing. Under rainfall deficit conditions, upland rice sown on U. brizantha straw shows higher profitability rates than when sown on U. ruziziensis. When there is a possibility of rainfall deficit, U. brizantha, as a cover plant, results in a greater economic security for upland rice producers.

The Water Requirements of Grapevines (Vitis vinifera L.) Under Climatic Conditions of Central Poland

The purpose of this study was to estimate the water needs of grapevines in central Poland in 1981-2010. Water needs were calculated by the plant coefficients, which were assumed according to the Doorenbos and Pruitt method. Reference evapotranspiration was assessed by the Blaney-Criddle’s equation, modified for Polish conditions. Rainfall deficit with the occurrence probability of normal, medium dry and very dry years was determined by the Ostromęcki’s method. Water needs of grapevines during the growing season was 434 mm. Upward time trend in the water needs both in the periods May-October and June-August was estimated. Temporal variability in the water needs was significant for most of the provinces. The rainfall deficit was recorded with the occurrence probability of normal as well as medium or very dry years in the entire study area. Due to climate changes, vineyards will require irrigation in the near future. This research significantly broadens and refines the knowledge about the water needs of grapevines in central Poland, which will allow the design of resource-efficient irrigation programs for grapevines in the studied region of Poland.

Indian monsoon derailed by a North Atlantic wavetrain

The forecast of Indian monsoon droughts has been predicated on the notion of a season-long rainfall deficit linked to a warm equatorial Pacific. Here we show that nearly half of all droughts over the past century differ from this paradigm in that they (i) occur when Pacific temperatures are near-neutral and (ii) are subseasonal phenomena, characterized by an abrupt decline in late-season rainfall. This severe subseasonal rainfall deficit can be associated with a Rossby wave from mid-latitudes. Specifically, we find that the interaction of upper-level winds with an episodic North Atlantic vorticity anomaly results in a wavetrain that curves toward East Asia, disrupting the monsoon. This atmospheric teleconnection offers an avenue for improved predictability of droughts, especially in the absence of telltale signatures in the Pacific.

Increasing risk of another Cape Town “Day Zero” drought in the 21st century

Three consecutive dry winters (2015–2017) in southwestern South Africa (SSA) resulted in the Cape Town “Day Zero” drought in early 2018. The contribution of anthropogenic global warming to this prolonged rainfall deficit has previously been evaluated through observations and climate models. However, model adequacy and insufficient horizontal resolution make it difficult to precisely quantify the changing likelihood of extreme droughts, given the small regional scale. Here, we use a high-resolution large ensemble to estimate the contribution of anthropogenic climate change to the probability of occurrence of multiyear SSA rainfall deficits in past and future decades. We find that anthropogenic climate change increased the likelihood of the 2015–2017 rainfall deficit by a factor of five to six. The probability of such an event will increase from 0.7 to 25% by the year 2100 under an intermediate-emission scenario (Shared Socioeconomic Pathway 2-4.5 [SSP2-4.5]) and to 80% under a high-emission scenario (SSP5-8.5). These results highlight the strong sensitivity of the drought risk in SSA to future anthropogenic emissions.

Detecting Groundwater Level Changes with Radar Interferometry

<p>The Dutch are known for their dewatered peat pastures known as polders. These pastures are used for heavy agricultural and have to be continuously drained to compensate for the subsiding top layer due to oxidation. Additionally, the top part of the peat soil responds to changes in temperature and precipitation. Driven by moisture changes, the peat soils shrink as water is evaporated during dry, warm periods, while they swell in periods with lots of precipitation. During these dry periods, the groundwater level drops as well, mirroring the behavior of the surface. As the groundwater level drops, more organic material is exposed to air and more greenhouse gases are emitted. Monitoring the movement of the surface of the pasture could provide indirect measurements of the groundwater level and used to reveal areas that are more or less affected by a rainfall deficit. Efforts to reduce emissions can then be focused on more vulnerable areas. However, this dynamical behavior is hard to monitor with conventional geodetic means, as it is near impossible to install the required benchmarks on the soft surface of the pastures, which are needed for repeated surveying.  </p><p>Radar Interferometry presents an opportunity to observe this dynamic behavior without the need of installing equipment. The Sentinel-1a/b satellites pass the Dutch peat soils four times per week, providing the data necessary to observe the shrinking and swelling of the soils. We applied the technique to two study areas in the Netherlands, one between Delft and Rotterdam, where most of the pastures are situated on peat or peaty soils, and one above Zwolle in the center of Netherlands, near Staphorst, a peat-rich area. We processed all radar acquisitions between 2017 and 2019, which were averaged to 200 by 200 meter square windows to suppress noise. This is than further processed to obtain deformation time series. Based on these time series, areas more vulnerable to droughts were identified. Notably, 2018 – a very dry year, with a very large rainfall deficit – caused significantly more shrinkage than observed in 2017. We estimate that some areas shrunk up to 50 percent more. The associated drop in groundwater level exposed fresh peat to air for the first time, potentially increasing the emission of greenhouse gases significantly.</p><p>Climate change exposes peat soils to new and more extreme weather conditions. Radar Interferometry can monitor the impact of these conditions on the soils and can be used to reduce greenhouse emissions more effectively.</p>

Water needs of Sambucus nigra L. grown in the reclaimed areas in Poland

The goal of this study was to assess the water needs of elderberry. The investigation included elderberry plants that had been planted in land reclamation areas more than three years earlier. The water needs were evaluated for 5 agro-climatic regions of Poland. The calculations were based on the observation of meteorological conditions in the years 1981-2010 for the period from June 1 to July 31. To determine the water needs, the plant coefficient method was applied. The Blaney-Criddle formula, which was modified for Polish conditions by Żakowicz (2010), was used to calculate the reference evapotranspiration. The plant coefficients of elderberry, adapted to the reference evapotranspiration, were adjusted to Żakowicz’s method. The rainfall deficit with the probability of occurrence: N50%, N25% and N10%, was assessed in accordance with Ostromęcki’s method. The highest water needs of elderberry occurred in central-north-west (264 mm) and central-east (262 mm) Poland, while the lowest (244 mm) in the south-east region. In June, the highest total monthly water needs (119 mm) were noted for south-west Poland, whereas the lowest (107 mm) for the south-east region. In June and July, except for the central-north-west region, an upward time trend of water needs was noted throughout Poland. In June and July, the highest value (135 mm) of rainfall deficit N50% and N25% was estimated for the central-north-west region, while the highest rainfall deficit N10% (269 mm) for central-east Poland. The results of the presented research find application in the planning of irrigation treatments for elderberry in Poland.

Rainfall, evapotranspiration and rainfall deficit trend in Alor Setar, Malaysia

Rainfall and potential evapotranspiration are important variables in water balance study. Rainfall data were obtained from Malaysian Meteorological Department while estimates of potential evapotranspiration were calculated using Penman-Monteith method. Trend analysis of monthly and annual rainfall, potential evapotranspiration and rainfall deficit are essential to manage irrigation system in agricultural systems. This is because changes in trend of these parameters may affect the water cycle and ecosystem. Annual and monthly values of these variables were analysed from 1980-2009. Results indicated increasing trends of 16.2 mm yr-1 and 3.01 mm yr-1 for both annual rainfall and potential evapotranspiration, respectively. Consequently, these trends resulted in annual rainfall deficit of 1.69 mm per year.

Rainfall index insurance for corn farmers in Shandong based on high-resolution weather and yield data

Purpose The purpose of this paper is to present the development of cumulative rainfall deficit (CRD) indices for corn in Shandong Province, China, based on high-resolution weather (county, 1980-2011) and yield data (township, 1989-2010) for five counties in Tai’an prefecture. Design/methodology/approach A survey with farming households is undertaken to obtain local corn prices and production costs to compute the sum insured. CRD indices are developed for five corn-growth phases. Rainfall is spatially interpolated to derive indices for areas that are outside a 25 km radius from weather stations. To lower basis risk, triggers and exits of the payout functions are statistically determined rather than relying on water requirement levels. Findings The results show that rainfall deficits in the main corn-growth phases explain yield reductions to a satisfying degree, except for the emergence phase. Correlation coefficients between payouts of the CRD indices and yield reductions reach 0.86-0.96 and underline the performance of the indices with low basis risk. The exception is SA-Xintai (correlation 0.71) where a total rainfall deficit index performs better (0.87). Risk premium rates range from 5.6 percent (Daiyue) to 12.2 percent (SA-Xintai) and adequately reflect the drought risk. Originality/value This paper suggests that rainfall deficit indices can be used in the future to complement existing indemnity-based insurance products that do not cover drought for corn in Shandong or for CRD indices to operate as a new insurance product.

Model-based study of the role of rainfall and land use–land cover in the changes in the occurrence and intensity of Niger red floods in Niamey between 1953 and 2012

Since 1950, the Niger River basin has gone through three main climatic periods: a wet period (1950–1960), an extended drought (1970–1980) and since 1990 a recent partial recovery of annual rainfall. Hydrological changes co-occur with these rainfall fluctuations. In most of the basin, the rainfall deficit caused an enhanced discharge deficit, but in the Sahelian region the runoff increased despite the rainfall deficit. Since 2000 the Sahelian part of the Niger has been hit by an increase of flood hazards during the so-called red flood period. In Niamey city, the highest river levels and the longest flooded period ever recorded occurred in 2003, 2010, 2012 and 2013, with heavy casualties and property damage. The reasons for these changes, and the relative role of climate versus land use–land cover (LULC) changes are still debated and are investigated in this paper. The evolution of the Niger red flood in Niamey from 1950 to 2012 is analysed based on long-term records of rainfall (three data sets based on in situ and/or satellite data) and discharge, and a hydrological model. The model is first run with the present LULC conditions in order to analyse solely the effect of rainfall variability. The impact of LULC and drainage area modification is investigated in a second step. The simulations based on the current surface conditions are able to reproduce the observed trend in the red flood occurrence and intensity since the 1980s. This has been verified with three independent rainfall data sets and implies that rainfall variability is the main driver for the red flood intensification observed over the last 30 years. The simulation results since 1953 have revealed that LULC and drainage area changes need to be invoked to explain the changes over a 60-year period.