Browsing by Author "Stocker, Benjamin D."

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Reconciling Precipitation with Runoff: Observed Hydrological Change in the Midlatitudes
(2015-12) Osborne, Joe M.; Lambert, F. Hugo; Groenendijk, Margriet; Harper, Anna B.; Koven, Charles D.; Poulter, Benjamin; Pugh, Thomas A. M.; Sitch, Stephen; Stocker, Benjamin D.; Wiltshire, Andy; Zaehie, Sonke
Century-long observed gridded land precipitation datasets are a cornerstone of hydrometeorological research. But recent work has suggested that observed Northern Hemisphere midlatitude (NHML) land mean precipitation does not show evidence of an expected negative response to mid-twentieth-century aerosol forcing. Utilizing observed river discharges, the observed runoff is calculated and compared with observed land precipitation. The results show a near-zero twentieth-century trend in observed NHML land mean runoff, in contrast to the significant positive trend in observed NHML land mean precipitation. However, precipitation and runoff share common interannual and decadal variability. An obvious split, or breakpoint, is found in the NHML land mean runoffâ€“precipitation relationship in the 1930s. Using runoff simulated by six land surface models (LSMs), which are driven by the observed precipitation dataset, such breakpoints are absent. These findings support previous hypotheses that inhomogeneities exist in the early-twentieth-century NHML land mean precipitation record. Adjusting the observed precipitation record according to the observed runoff record largely accounts for the departure of the observed precipitation response from that predicted given the real-world aerosol forcing estimate, more than halving the discrepancy from about 6 to around 2 W mâˆ’2. Consideration of complementary observed runoff adds support to the suggestion that NHML-wide early-twentieth-century precipitation observations are unsuitable for climate change studies. The agreement between precipitation and runoff over Europe, however, is excellent, supporting the use of whole-twentieth-century observed precipitation datasets here.
The terrestrial carbon budget of South and Southeast Asia
(2016-10) Cervarich, Matthew; Shu, Shijie; Jain, Atul K.; Arneth, Almut; Canadell, Josep; Friedlingstein, Pierre; Houghton, Richard A; Kato, Etsushi; Koven, Charles D.; Patra, Prabir K.; Poulter, Benjamin; Sitch, Stephen; Stocker, Benjamin D.; Viovy, Nicolas; Wiltshire, Andy; Zeng, Ning
Accomplishing the objective of the current climate policies will require establishing carbon budget and flux estimates in each region and county of the globe by comparing and reconciling multiple estimates including the observations and the results of top-down atmospheric carbon dioxide (CO2) inversions and bottom-up dynamic global vegetation models. With this in view, this study synthesizes the carbon source/sink due to net ecosystem productivity (NEP), land cover land use change (E-LUC), fires and fossil burning (E-FIRE) for the South Asia (SA), Southeast Asia (SEA) and South and Southeast Asia (SSEA = SA + SEA) and each country in these regions using the multiple top-down and bottom-up modeling results. The terrestrial net biome productivity (NBP = NEP - E-LUC - E-FIRE) calculated based on bottom-up models in combination with E-FIRE based on GFED4s data show net carbon sinks of 217 +/- 147, 10 +/- 55, and 227 +/- 279 TgC yr(-1) for SA, SEA, and SSEA. The top-down models estimated NBP net carbon sinks were 20 +/- 170, 4 +/- 90 and 24 +/- 180 TgC yr(-1). In comparison, regional emissions from the combustion of fossil fuels were 495, 275, and 770 TgC yr(-1), which are many times higher than the NBP sink estimates, suggesting that the contribution of the fossil fuel emissions to the carbon budget of SSEA results in a significant net carbon source during the 2000s. When considering both NBP and fossil fuel emissions for the individual countries within the regions, Bhutan and Laos were net carbon sinks and rest of the countries were net carbon source during the 2000s. The relative contributions of each of the fluxes (NBP, NEP, ELUC, and EFIRE, fossil fuel emissions) to a nation\'s net carbon flux varied greatly from country to country, suggesting a heterogeneous dominant carbon fluxes on the country-level throughout SSEA.