Historical agricultural droughts from the INternational Pro pluvia ROgation database

<p>We present the INPRO (INternational Pro pluvia ROgation) database, the first international initiative to compile and share information on pro pluvia rogation ceremonies. Rogations are religious rites celebrated in supplication to gods for changing the environmental or social risks brought to their communities. Pro pluvial rogations have the specific objective to obtain rainfall during drought periods. This proxy has been used to understand drought variability in the pre-instrumental period, to generate precipitation or atmospheric circulation modes reconstructions, to validate natural proxies, or to understand the social consequences of droughts, mainly during the last 500 years. Different methodologies have been used in the literature to extract the climate signal from this proxy. Here, we evaluate the pros and cons of these methodologies, with special attention on methodologies based on the date of the celebration, since it is the main variable provided by INPRO. Important questions to take advantage of INPRO database are discussed e.g. types of documentary sources (primary or secondary), time resolution (daily, monthly, seasonally or yearly) or seasonality (related with agricultural labours). Finally, we provide recommendations for the use of IMPRO depending on the different research objectives e.g. case studies, drought reconstruction, proxies validation. Currently INPRO database has more than 3500 dates of pro pluvia ceremonies in 153 locations of 11 countries (Mexico, Guatemala, Ecuador, Peru, Chile, Argentina, Portugal, Spain, France, Italy, Philippines). The database covers the period from 1333 to 1949, being the 18<sup>th</sup> century when more information is available. INPRO database can be freely accessed and visualized via http://inpro.unizar.es/.</p>

Advances in Land Surface Models and Indicators for Drought Monitoring and Prediction

Millions of people across the globe are affected by droughts every year, and recent droughts have highlighted the considerable agricultural impacts and economic costs of these events. Monitoring the state of droughts depends on integrating multiple indicators that each capture particular aspects of hydrologic impact and various types and phases of drought. As the capabilities of land-surface models and remote sensing have improved, important physical processes such as dynamic, interactive vegetation phenology, groundwater, and snow pack evolution now support a range of drought indicators that better reflect coupled water, energy and carbon cycle processes. In this work, we discuss these advances, including newer classes of indicators that can be applied to improve the characterization of drought onset, severity and duration. We utilize a new model-based drought reconstruction to illustrate the role of dynamic phenology and groundwater in drought assessment. Further, through case studies on flash droughts, snow droughts, and drought recovery, we illustrate the potential advantages of advanced model physics and observational capabilities, especially from remote sensing, in characterizing droughts.

The Driftless Oaks: A new network of tree-ring chronologies to improve regional perspectives of drought in the Upper Midwest, USA

New and updated multi-century tree-ring chronologies from living oak trees, remnants, and archeological beams from across the Driftless Area of southwest Wisconsin and northeast Iowa, USA, were developed to fill a spatial gap in the network of available tree-ring chronologies. We produced a robust 303-year summer drought reconstruction (June–August Palmer’s Modified Drought Index (PMDI): r 2 = 0.45) that identified clusters of extreme droughts and pluvials (PMDI ≤ –4.0 or ≥ 4.0) in the early 1700s and more even distributions of drought conditions, with the exception of the post 1930s period when drought became relatively infrequent. Compared to the Living Blended Drought Atlas (LBDA) and the North American Drought Atlas (NADA), our reconstruction more accurately represented moderate moisture conditions across the Driftless Area, the NADA and LBDA more closely represented extreme pluvials, and our reconstruction and the LBDA better represented extreme drought years. The three reconstructions largely captured the same high-frequency variability in drought conditions and differed most at low frequencies. Significant correlations were identified between our reconstruction and corn ( r = 0.30, n = 91, p = 0.002) and soybean ( r = 0.25, n = 81, p = 0.012) yields, with the strength of the correlations increasing over recent decades suggesting a tighter coupling of interannual climate variability and crop productivity in the region. Superposed epoch analyses indicated significantly wetter conditions in the Driftless Area two years after major volcanic eruptions. In the context of long-term climatic variability, the Driftless Oaks drought reconstruction demonstrated that drought and pluvial conditions more extreme than those experienced during the instrumental record have occurred in the past.

Validation of reconstructed hydroclimate variables for past drought assessment

<p>In present paper we compare the reconstructed gridded seasonal precipitation (P) and temperature (T) for Europe [1,2] to the available station data from the GHCN [3,4] network going back to 1800. The basic statistical properties at various time-scales ranging from 1/4 to 30 years are examined. It is shown, that there are significant biases in the reconstructed P and T and the bias in mean and variability considerably vary over the time-scales. The same applies for considered drought indices. We further investigate how the simulation of hydrological model driven by reconstructed data compares to that based on station data and runoff from GRDC database. In addition, a set of data-driven methods is used to link the reconstructed and observed P and T data to observed runoff, the results are validated and a reconstruction back to 1500 is provided. Finally, we check to what extent the raw proxy data can be used for drought reconstruction.</p><p>[1] https://doi.org/10.1007/s00382-005-0090-8<br>[2] https://doi.org/10.1126/science.1093877<br>[3] https://doi.org/10.1175/JCLI-D-18-0094.1<br>[4] doi:10.7289/V5X34VDR</p>

Long-term (1870-2018) drought reconstruction in India

<p>Droughts in India affect food production, gross domestic product (GDP), livelihood, and socio-economic condition of a large population associated with agriculture. Recent drought (2015-2018) caused groundwater depletion and affected about one-fourth of the Indian population. However, it remains unclear if the drought of 2015-2018 was among the most severe droughts that occurred in India. Here we use a long-term (1870-2018) data to identify the top five ("deadly") meteorological/hydrological droughts based on overall severity score in the last century and half period. Out of a total of 18 meteorological droughts, the deadly droughts occurred in 1899, 1876, 2000, 1918, and 1965. Similarly, the deadly hydrological droughts occurred in 1899, 2000, 1876, 1965, and 1918 during 1870-2018. All the five deadly droughts were associated with the positive phase of El Nino Southern Oscillations (ENSO). Results show that the relationship between ENSO and monsoon (June to September) precipitation in India has weakened while the role of Indian and Atlantic Oceans has strengthened during the recent decades. Notwithstanding the longest (41 months) duration, the 2015-2018 drought did not feature among the deadly droughts. The 2015-2018 drought affected surface (reservoir storage) and groundwater availability in both southern and northern parts of India and was linked to El-Nino and Indian Ocean Dipole. Droughts and rapidly declining groundwater together can pose serious challenge to ensure fresh water security in India.</p>