Climate Outlook Research Articles

Analog (Nonlinear) Forecasts of the Southern Oscillation Index Time Series

Abstract A nonlinear time series forecasting scheme developed by Sugihara and May has been applied to the Southern Oscillation index. Although forecast skill is comparable only to persistence or linear (autoregressive) methods, the scheme has the advantage of identifying close analogs to the current situation, if these exist. The operational implementation of the scheme in the Seasonal Climate Outlook issued by the National Climate Centre of the Australian Bureau of Meteorology is described and its performance during the 1991/92 El Nino–Southern Oscillation event is examined.

EVALUATION OF GREAT LAKES NET BASIN SUPPLY FORECASTS1

ABSTRACT: Evaluation of the Great Lakes Environmental Research Laboratory's (GLERL's) physically‐based monthly net basin supply forecast method reveals component errors and the effects of model improvements for use on the Laurentian Great Lakes. While designed for probabilistic outlooks, it is assessed for giving deterministic outlooks along with other net basin supply forecast methods of the U.S. Army Corps of Engineers and Environment Canada, and with a stochastic approach commissioned by the Corps. The methods are compared to a simple clima‐tological forecast and to actual time series of net basin supplies. Aetual net basin supplies are currently determined by estimating all components directly, instead of as water‐balance residuals. This is judged more accurate and appropriate for both forecasting and simulation. GLERL's physically‐based method forecasts component supplies while the other methods are based on residual supplies. These other methods should be rederived to be based on component supplies. For each of these other methods, differences between their outlooks and residual supplies are used as error estimates for the rederived methods and component supplies. The evaluations are made over a recent period of record high levels followed by a record drought. Net basin supply outlooks are better than climatology, and GLERL's physically‐based method performs best with regard to either component or residual net basin supplies. Until advances are made in long‐range climate outlooks, deterministic supply outlooks cannot be improved significantly.

Consequences of winter tropical pressure anomalies in the Australian region

AbstractWe have performed three general circulation model (GCM) experiments with a view to isolating the direct thermal effects of imposed sea‐surface temperature (SST) anomaly patterns to the north of Australia from the dynamic effects associated with the circulation changes they induce. We have done this by a novel technique of adding bias terms to the pressure‐tendency equation but leaving all other aspects of the model unchanged. The nature of the three pressure ‘nudging’ terms were designed so that in long model runs the simulated sea‐level reductions would be similar to those induced in the SST anomaly experiments performed previously. Hence, we have forced low‐level circulation anomalies without imposing any direct surface thermal forcing. The results are compared with standard runs performed with SST forcing.The changes in evaporation in the Australian region were rather different in the comparable pressure‐forcing and SST‐forced experiments. However, most of the parameters considered here responded to the surface‐pressure forcing in a very similar way to that due to ocean‐temperature forcing considered in our earlier study. This was true, in particular, for winter precipitation over Australia. The results suggest that, at least in the Australian tropics, the apparently large impacts of SST anomalies are associated fundamentally with the anomalous circulations they set up rather than the direct impact of the heated ocean waters themselves. We find, as have others, that precipitation anomalies are associated closely with changes of the low‐level convergence of moisture. Indeed, an intriguing finding from our present study is that anomalies of evaporation and precipitation assume opposite signs over most of the domain.Analyses with the comprehensive ocean‐atmosphere data set (COADS) imply that there is some persistence of winter tropical sea‐level pressure in the Australian region, independent of the local endurance of SST. Such persistence may provide some independent skill for Australian winter climate outlooks.

Comment on “Soil moisture estimation by the neutron scattering method in Britain”: by J. P. Bell and J. S. G. Mcculloch (J. of Hydrology 4 (1966) 254–263)

The usefulness of climate information for agricultural risk management hinges on its availability and relevance to the producer when climate-sensitive decisions are being made. Climate information providers are challenged with the task of balancing forecast availability and lead time with acceptable forecast skill, which requires an improved understanding of the timing of agricultural decision making. Achieving a useful balance may also require an expansion of inquiry to include use of non-forecast climate information (i.e. historical climate information) in agricultural decision making. Decision calendars have proven valuable for identifying opportunities for using different types of climate information. The extent to which decision-making time periods are localized versus generalized across major commodity-producing regions is yet unknown, though, which has limited their use in climate product development. Based on a 2012 survey of more than 4770 agricultural producers across the U.S. Corn Belt region, we found variation in the timing of decision-making points in the crop year based on geographic variation as well as crop management differences. Many key decisions in the cropping year take place during the preceding fall and winter, months before planting, raising questions about types of climate information that might be best inserted into risk management decisions at that time. We found that historical climate information and long term climate outlooks are less influential in agricultural risk management than current weather, short term forecasts, or monthly climate projections, even though they may, in fact, be more useful to certain types of decision making.