Projected changes in meteorological drought risk under future climate change scenarios

(Part II)

Christoph Menz

RDII

# Outline - Recap - Change in dry spell duration and frequency - Change in dry spell intensity - Conclusion

# Recap

## Recap - Based on Regional Climate Model - **RCM** - simulations published within CORDEX-EUR11 framework - Numerical models solving **physical equations of motion** on a limited domain with boundary information from global climate models - Bias Adjusted using trend preserving empirical/parametric quantile mapping

- Timeframe covered: **1971-2100** - Temporal resolution: **daily** - Spatial Resolution: **0.11°** (≈**12.5km**) - Variables: **Temperature** (minimum, average and maximum) and **Precipitation** - Total model simulations: **72**

RCP2.6: **18** RCP4.5: **17** RCP8.5: **37**

## Climate Change Projections

Temperature

--- 2071-2100 vs. 1981-2010 --- RCP8.5 ---

Precipitation

Evapotranspiration

--- 37 simulations --- significance level \begin{align} \alpha = 0.3 \end{align} ---

Climatic Water Balance

Change in dry spell duration and frequency

## Change in Number of Dry Days

- At least 7 consecutive days with precipitation below 1.0mm

- **North to south gradient** resembling precipitation change

- **Dry regions** and **seasons** get **drier**

--- 2071 - 2100 vs. 1981 - 2010 RCP8.5 significance level $\hphantom{a}\alpha = 0.3$ ---

## Dry Spell Return Period

Annual 1981-2100

Change in dry spell intensity

## Change in SPEI

- Standardized Precipitation Evapotranspiration Index

- **North to south gradient**, similar to dryDays and precipitation change

- **Longer time scales** show **stronger change**

--- 2071 - 2100 vs. 1981 - 2010 RCP8.5 significance level $\hphantom{a}\alpha = 0.3$ ---

## SPEI change in time - Development of SPEI for a single grid point - Smooth time series with decadal running window average - Determine threshold, when SPEI turn negative

--- 1986-2096 RCP8.5 37 simulations ---

85 percentile

100 x resampled

## SPEI change in time

- Decade when ensemble **SPEI** turns **negative** on **average**

- Most of **Mediterranen** turns **negative SPEI** within the **first half of the 21st century**

- **Central** and **northern Europe** still in climatological **positive SPEI** state

- **Longer time scale SPEI** appears **earlier** and propagates **faster** northward

--- 85% threshold significance level $\alpha = 0.15$ ---

RCP2.6

RCP4.5

RCP8.5

3-months

6-months

12-months

24-months

## SPEI future change vs. observed change

3-months

6-months

12-months

24-months

2071-2100
vs.
1981-2010

Projections

## SPEI future change vs. observed change

3-months

6-months

12-months

24-months

2001-2010
vs.
1981-2000

Observations

2071-2100
vs.
1981-2010

Projections

Conclusion

## Conclusion

- **Temperature** (0.8 to 5.3K) and **evapotranspiration** (0.04 to 0.38mm/d) will **increase significantly** throughout Europe until 2100

- **Precipitation increases in north** (-0.2 to 0.3mm/d) and **decreases in south**, increase in north compensates for increase in evapotranspiration

- All drought indices show similar pattern as precipitation change

- Number of **dry days increases in south** (up to 14 days), especially in dry seasons

- **Extreme drought events increase only slightly** in Mediterranen (5-10 days), return periods roughly halve

- **SPEI increases significantly** (down to -1.0/-1.3/-1.6/-2.1 for 3/6/12/24 months) in southern Europe, turning climatilogical negative in the first half of the 21st century

- **SPEI decrease at higher time scale** show **stronger decrease**, **propagestes further north** and **changes earlier**