Correcting Thornthwaite potential evapotranspiration using a global grid of local coefficients to support temperature-based estimations of reference evapotranspiration and aridity indices

Thornthwaite’s formula is globally an optimum candidate for large scale applications of potential evapotranspiration and aridity assessment at different climates and landscapes since it has the lower data requirements compared to other methods and especially from the ASCE-standardized reference evapotranspiration (former FAO-56), which is the most data demanding method and is commonly used as benchmark method. The aim of the study is to develop a global database of local coefficients for correcting the formula of monthly Thornthwaite potential evapotranspiration (Ep) using as benchmark the ASCE-standardized reference evapotranspiration method (Er). The validity of the database will be verified by testing the hypothesis that a local correction coefficient, which integrates the local mean effect of wind speed, humidity and solar radiation, can improve the performance of the original Thornthwaite formula. The database of local correction coefficients was developed using global gridded temperature and Er data of the period 1950–2000 at 30 arc-sec resolution (~1 km at equator) from freely available climate geodatabases. The correction coefficients were produced as partial weighted averages of monthly Er / Ep ratios by setting the ratios’ weight according to the monthly Er magnitude and by excluding colder months with monthly values of Er or Ep < 45 mm month−1 because their ratio becomes highly unstable for low temperatures. The validation of the correction coefficients was made using raw data from 525 stations of Europe, California-USA and Australia including data up to 2020. The validation procedure showed that the corrected Thornthwaite formula Eps using local coefficients led to a reduction of RMSE from 37.2 to 30.0 mm m−1 for monthly and from 388.8 to 174.8 mm y−1 for annual step estimations compared to Ep using as benchmark the values of Er method. The corrected Eps and the original Ep Thornthwaite formulas were also evaluated by their use in Thornthwaite and UNEP (United Nations Environment Program) aridity indices using as benchmark the respective indices estimated by Er. The analysis was made using the validation data of the stations and the results showed that the correction of Thornthwaite formula using local coefficients increased the accuracy of detecting identical aridity classes with Er from 63 % to 76 % for the case of Thornthwaite classification, and from 76 % to 93 % for the case of UNEP classification. The performance of both aridity indices using the corrected formula was extremely improved in the case of non-humid classes. The global database of local correction factors can support applications of reference evapotranspiration and aridity indices assessment with the minimum data requirements (i.e. temperature) for locations where climatic data are limited. The global grids of local correction coefficients for Thornthwaite formula produced in this study are archived in PANGAEA database andcan be assessed using the following link: https://doi.pangaea.de/10.1594/PANGAEA.932638 (Aschonitis et al., 2021).

Deoxynivalenol Occurrence in Triticale Crops in Romania during the 2012–2014 Period with Extreme Weather Events

This article aims to evaluate deoxynivalenol occurrence in triticale crops in Romania in years with extreme weather events (2012: Siberian anticyclone with cold waves and heavy snowfall; 2013 and 2014: “Vb” cyclones with heavy precipitation and floods in spring). The deoxynivalenol level in triticale samples (N = 236) was quantified by ELISA. In Romania, the extreme weather events favoured deoxynivalenol occurrence in triticale in Transylvania and the southern hilly area (44–47°N, 22–25°E) with a humid/balanced-humid temperate continental climate, luvisols and high/very high risk of floods. Maximum deoxynivalenol contamination was lower in the other regions, although heavy precipitation in May–July 2014 was higher, with chernozems having higher aridity. Multivariate analysis of the factors influencing deoxynivalenol occurrence in triticale showed at least a significant correlation for all components of variation source (agricultural year, agricultural region, average of deoxynivalenol, average air temperature, cumulative precipitation, soil moisture reserve, aridity indices) (p-value < 0.05). The spatial and geographic distribution of deoxynivalenol in cereals in the countries affected by the 2012–2014 extreme weather events revealed a higher contamination in Central Europe compared to southeastern and eastern Europe. Deoxynivalenol occurrence in cereals was favoured by local and regional agroclimatic factors and was amplified by extreme weather events.

Aridity Indices to Assess Desertification Susceptibility: A Methodological Approach Using Gridded Climate Data

Desertification is a land degradation phenomenon with dire and irreversible consequences, affecting different regions of the world. Assessment of spatial susceptibility to desertification requires long-term series of precipitation (P) and evapotranspiration (PET). An approach to desertification analysis is the use of spatially gridded time series of air temperature and precipitation, derived from spatial interpolation of in situ measurements and available globally. The aim of this article was to estimate the susceptibility to desertification over Southeast Brazil using monthly gridded data from the Global Precipitation Climatology Centre (GPCC), and from the Global Historical Climatology Network (GHCN). Two indices were used to estimate desertification susceptibility: the aridity index Ia (P/PET) and D (PET/P). Validation of these datasets was performed using in situ observations (1961—2010) from the National Institute of Meteorology (INMET) – (68 weather stations). Determination coefficient (r²) and the Willmott’s coefficient of agreement (d) between gridded and observed data revealed satisfactory accuracy and precision for grids of precipitation (r2 > 0.93, d > 0.90), air temperature (r2 > 0.94, d > 0.53) and PET (r2 > 0.93, d > 0.63). Areas susceptible to desertification were identified by the index Ia over the Northern regions of Minas Gerais and Rio de Janeiro states. No areas susceptible to desertification were identified using the index D. However, both indices indicated large areas of dry sub-humid climate, which can be strongly affected by drought conditions. Overall, climate gridded variables presented good precision and accuracy when used to identify areas susceptible to desertification.

Were late Gomphotheres (Plio-Pleistocene) of the Siwaliks at more Stress as Compared to early Gomphotheres (middle to late Miocene)?

Gomphotheres existed in the Siwaliks from the middle Miocene (14.2Ma) to the middle Pleistocene (0.8Ma) and became extinct later on. In this paper, we tried to discuss the reasons of such extinction of gomphotheres in the lower Pleistocene time span by considering Linear Enamel Hypoplasia (LEH) among 114 isolated tooth samples to assess whether ecological changes correlate with the stress factor in gomphotheres. For this purpose, the Siwalik gomphotheres were divided into two Groups viz. early gomphotheres (middle Miocene to late Miocene) and late gomphotheres (Pliocene to middle Pleistocene). We presented the hypothesis, that as the gomphotheres are characterized by the brachydonty and relied on browsing for their feeding while inhabiting the semi forest land setting thus, expected to have higher stress in Plio-Pleistocene time span as vegetational change around ~6 Ma may have exerted stress on late gomphotheres. The results for the occurrence of frequency of LEH indicated severe ecological stress in late gomphotheres (33%). The significant differences were found (P < 0.05) among the early gomphotheres and late gomphotheres which can be correlated to the vegetational change from C3 to C4, higher aridity indices and intensified seasonality after the late Miocene vegetational shift which may have resulted in substantial faunal turnover, extinction and speciation. We assume that such palaeoecological changes forced a competition with more pronounced grazers like of family Elephantidae and Bovidae resulting in extinction of gomphotheres during the late Pleistocene in the Siwaliks of Pakistan.