The great Australian drought: 1982-1983*

The Warming Climate Aggravates Atmospheric Nitrogen Pollution in Australia

Australia is a warm country with well-developed agriculture and a highly urbanized population. How these specific features impact the nitrogen cycle, emissions, and consequently affect environmental and human health is not well understood. Here, we find that the ratio of reactive nitrogen (N r ) losses to air over losses to water in Australia is 1.6 as compared to values less than 1.1 in the USA, the European Union, and China. Australian N r emissions to air increased by more than 70% between 1961 and 2013, from 1.2 Tg N yr-1 to 2.1 Tg N yr-1. Previous emissions were substantially underestimated mainly due to neglecting the warming climate. The estimated health cost from atmospheric N r emissions in Australia is 4.6 billion US dollars per year. Emissions of N r to the environment are closely correlated with economic growth, and reduction of N r losses to air is a priority for sustainable development in Australia.

A new global database of meteorological drought events from 1951 to 2016

STUDY REGION

This study has three spatial scales: global (0.5°), macro-regional, and country scale. The database of drought events has specific entries for each macro-region and country.

STUDY FOCUS

We constructed a database of meteorological drought events from 1951 to 2016, now hosted by the Global Drought Observatory of the European Commission's Joint Research Centre. Events were detected at macro-regional and country scale based on the separate analysis of the Standardized Precipitation-Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) at different accumulation scales (from 3 to 72 months), using as input the Global Precipitation Climatology Centre (GPCC) and Climatic Research Unit (CRU) Time Series datasets. The database includes approximately 4800 events based on SPEI-3 and 4500 based on SPI-3. Each event is described by its start and end date, duration, intensity, severity, peak, average and maximum area in drought, and a special score to classify 52 mega-droughts.

NEW HYDROLOGICAL INSIGHTS FOR THE REGION UNDER STUDY

We derived trends in drought frequency and severity, separately for SPI and SPEI at a 12-month accumulation scale, which is usually related to hydrological droughts. Results show several drought hotspots in the last decades: Amazonia, southern South America, the Mediterranean region, most of Africa, north-eastern China and, to a lesser extent, central Asia and southern Australia. Over North America, central Europe, central Asia, and Australia, the recent progressive temperature increase outbalanced the increase in precipitation causing more frequent and severe droughts.

Monitoring Drought Effects on Vegetation Productivity Using Satellite Solar-Induced Chlorophyll Fluorescence

Around the world, the increasing drought, which is exacerbated by climate change, has significant impacts on vegetation carbon assimilation. Identifying how short-term climate anomalies influence vegetation productivity in a timely and accurate manner at the satellite scale is crucial to monitoring drought. Satellite solar-induced chlorophyll fluorescence (SIF) has recently been reported as a direct proxy of actual vegetation photosynthesis and has more advantages than traditional vegetation indices (e.g., the Normalized Difference Vegetation Index, NDVI and the Enhanced Vegetation Index, EVI) in monitoring vegetation vitality. This study aims to evaluate the feasibility of SIF in interpreting drought effects on vegetation productivity in Victoria, Australia, where heat stress and drought are often reported. Drought-induced variations in SIF and absorbed photosynthetically active radiation (APAR) estimations based on NDVI and EVI were investigated and validated against results indicated by gross primary production (GPP). We first compared drought responses of GPP and vegetation proxies (SIF and APAR) during the 2009 drought event, considering potential biome-dependency. Results showed that SIF exhibited more consistent declines with GPP losses induced by drought than did APAR estimations during the 2009 drought period in space and time, where APAR had obvious lagged responses compared with SIF, especially in evergreen broadleaf forest land. We then estimated the sensitivities of the aforementioned variables to meteorology anomalies using the ARx model, where memory effects were considered, and compared the correlations of GPP anomaly with the anomalies of vegetation proxies during a relatively long period (2007–2013). Compared with APAR, GPP and SIF are more sensitive to temperature anomalies for the general Victoria region. For crop land, GPP and vegetation proxies showed similar sensitivities to temperature and water availability. For evergreen broadleaf forest land, SIF anomaly was explained better by meteorology anomalies than APAR anomalies. GPP anomaly showed a stronger linear relationship with SIF anomaly than with APAR anomalies, especially for evergreen broadleaf forest land. We showed that SIF might be a promising tool for effectively evaluating short-term drought impacts on vegetation productivity, especially in drought-vulnerable areas, such as Victoria.