Problems using downscaled scenarios in studies of climate effects. Lars Bakken - The EACC project Our first trials (and errors)* More scenarios? Better scenarios? Simple wheather manipulations? Wheather generators? *http://www.nlh.no/?avd=54

COUP Snow cover Water stress Soil moisture Soil erosion Plant growth Soil biology C- and N model Trace gas model Frost/thaw Driving data Soil temp. Water transport

The scenarios: Dynamic downscaling (HIRHAM) based on: - AOGCM ECHAM4/OPYC3 with the GSDIO integration - IPCC IS92a scenario The control period: 1980-99: Obs80-99 = Observed wheather 1980-99 Scen80-99= Simulated weather 1980-99 The future wheather: Scen30-49= simulated wheather 2030-49

Snow depth Frost depth And soil frost is somewhat more shallow Much less snow in a warmer climate

Colder soils in a warmer climate? More frequent freeze/thaw events in a warmer climate? Number of ”frost spells” in the soil:

The summer is more problematic: The Scenarios are wet and cold!

And the Scenarios have a peculiar distribution of rain:

The cool and wet summers delayed the phenological development The high and frequent precipitation resulted in moist grains => Much delayed grain harvest!

The high Scenario-precipitation in July-August resulted in much too high drainage and surface runoff High erosion!

High erosion in summer High early-spring erosion due to snow melt on frozen soil

Quo vadis? Don Quijote & Sancho Panza (Daumier)

Several scenarios => More uncertainty Longer scenarios => Better statistics But the climate models will gradually become better… - Simulations driven by climate scenarios tend to be anecdotic the simulations are not causally transparent general respons patterns cannot be ”extracted” The difference between two scenarios are multidimensional The simulated ecological processes are nonlinear To understand the reasons for contrasting results is difficult

Alternative 1: Simple manipulations of observed wheather Additive for temperature (seasonal og whole year) Multiplicative for prcipiation Or stochastic Factorial model experiments => interactions detected Winter temperature: ∆T winter= -1 0 +1 Summer temperature: ∆Tsummer = -1 0 +1 Winter precipitation : KPwinter = 0.9 1.0 1.1 Summer precipitation: KPsummer = 0.9 1.0 1.1 All combinations: 81 simulations

Wheather generators Based on existing weather => reliable weather ”quality” ? Parameterized by contrasting climate scenarios plausible combinations ? Many or long time periods simulated => Statistics will be OK