An Observational and Modeling Study of Regional Impacts of Climate Variability at Agricultural Scales
Radley
Horton, NASA GISS, rh142@columbia.edu
(Presenting)
Cynthia
Rosenzweig, NASA GISS, crosenzweig@giss.nasa.gov
Climate variability has large impacts on humans and their agricultural systems. Climate variability and its regional impacts are explored in NASA observations and NASA models for the current and future climate. The goals are to identify impacts of observed variability, assess model simulation of variability, and explore how climate variability and its impacts may change under enhanced greenhouse warming.
Multiple versions of NASA GISS Atmospheric General Circulation Models (AGCMs) are hindcast with observed sea surface temperatures (SST). Over a recent cycle of El Niño and La Niña, all versions produce appropriate local changes. SST forced model analysis is extended to multiple ENSO events and additional modes, with emphasis on key agricultural regions. Key findings are that the model can reproduce: 1) the spatial pattern associated with two additional related modes, the AO and NAO; and 2) rainfall features and dynamical features such as SLP gradients and wind in the study regions.
ENSO impacts are assessed in the region where the models show the most promise: Indonesia. Early rainy season precipitation and circulation, and same-season planting and harvesting dates, are shown to be sensitive to ENSO. The locus of ENSO convergence and rainfall anomalies is shown to be near the axis of rainy season establishment, defined as the 6-8 mm/day isohyet, an approximate threshold for irrigated rice cultivation. Circulation anomalies associated with ENSO are shown to be similar to those associated with rainfall anomalies, suggesting that long lead-time ENSO forecasts may allow more adaptation than ‘wait and see’ methods, with little loss of forecast skill.
Under doubled CO2, the model able to capture ENSO dynamics - an atmospheric model coupled to the Cane-Zebiak ocean model (‘C4’ here) - generates more El Niño-like mean conditions in the tropical Pacific. These changes produce a 4x larger increase in maximum precipitation with warming in C4 than an atmospheric model with a slab ocean (Q4), dramatically enhancing the Pacific Hadley and Walker circulations, and through positive feedbacks, increasing the global temperature.