Evidence that extreme rainfall intensity is increasing at the global scale has strengthened considerably in recent years. Research now indicates that the greatest increases are likely to occur in short-duration storms lasting less than a day, potentially leading to an increase in the magnitude and frequency of flash floods. This review examines the evidence for subdaily extreme rainfall intensification due to anthropogenic climate change and describes our current physical understanding of the association between subdaily extreme rainfall intensity and atmospheric temperature. We also examine the nature, quality, and quantity of information needed to allow society to adapt successfully to predicted future changes, and discuss the roles of observational and modeling studies in helping us to better understand the physical processes that can influence subdaily extreme rainfall characteristics. We conclude by describing the types of research required to produce a more thorough understanding of the relationships between local-scale thermodynamic effects, large-scale atmospheric circulation, and subdaily extreme rainfall intensity.

Vegetation change plays a critical role in the Earth's carbon (C) budget and its associated radiative forcing in response to anthropogenic and natural climate change 1-4 . Existing global estimates of aboveground biomass carbon (ABC) based on field survey data provide brief snapshots that are mainly limited to forest ecosystems 5-8 . Here we use an entirely new remote sensing approach to derive global ABC estimates for both forest and non-forest biomes during the past two decades from satellite passive microwave observations. We estimate a global average ABC of 362 PgC over the period 1998-2002, of which 65% is in forests and 17% in savannahs. Over the period 1993-2012, an estimated −0.07 PgC yr −1 ABC was lost globally, mostly resulting from the loss of tropical forests (−0.26 PgC yr −1 ) and net gains in mixed forests over boreal and temperate regions (+0.13 PgC yr −1 ) and tropical savannahs and shrublands (+0.05 PgC yr −1 ). Interannual ABC patterns are greatly influenced by the strong response of water-limited ecosystems to rainfall variability, particularly savannahs. From 2003 onwards, forest in Russia and China expanded and tropical deforestation declined. Increased ABC associated with wetter conditions in the savannahs of northern Australia and southern Africa reversed global ABC loss, leading to an overall gain, consistent with trends in the global carbon sink reported in recent studies 1,3,9 .Over the past two decades, the terrestrial biosphere has acted as a sink for atmospheric CO 2 , removing on average approximately 2.5 petagrams of carbon per year (PgC yr −1 ): equivalent to 25% of fossil fuel emissions 1-4 . Additional emissions from land-use change reduce the global net land sink to approximately 1.5 PgC yr −1 , with forests playing a dominant role 5 . Monitoring C stock changes over time can be used to determine which ecosystems and processes drive changes in C fluxes and to develop strategies for climate change mitigation. The existing global ABC estimates based on field survey data, such as the recent global synthesis by Pan et al. 5 , provide snapshots in time and are limited to forest ecosystems only. Estimating ABC using satellite remote sensing can provide a more consistent methodology and global coverage 6 . Although offering high spatial resolution, current remote sensing products have limited temporal frequency and record length at the global scale 6-8 .Here, we derive global ABC estimates for all vegetation types for the past two decades using an entirely new approach that uses satellite-based passive microwave data rather than the optical or radar observations used previously. The intensity of natural microwave radiation from the Earth is a function of its temperature, soil moisture and the shielding effect of water in aboveground vegetation biomass, including canopy and woody components 10-12 . The biomass signal is captured in the vegetation optical depth (VOD; refs 13,14). A distinct advantage of passive microwavederived VOD is that it remains sensitive to biomass variations at a ...

No abstract