1Instituto Pirenaico de Ecología, Consejo Superior de Investigaciones Científicas (IPE–CSIC), Zaragoza, Spain, 2Environmental Physics Laboratory, Universidade de Vigo,

Ourense, Spain, 3University of Gothenburg, GothenburgSweden

Sergio M. Vicente-Serrano1, Raquel Nieto2, Luis Gimeno2, Cesar Azorin-Molina3

Global changes in relative humidity: connection

with climate trends, humidity sources and

moisture transport processes.

STRONG IMPORTANCE IN SEVERAL ATMOSPHERIC PROCESSES

Vicente-Serrano, S.M. et al. (2014): Water Resources Research, 50, 8458

Simmons, A.J. et al (2010). J Geophys Res Atmos 115:D01110

Willett, K. M., et al. (2014): Clim. Past, 10, 1983

Dai, A. (2006): J. Climate, 19: 3589.

Sherwood and Fu (2014): Science, 343, 737.

Fu, Q., and S. Feng (2014), J. Geophys. Res. Atmos., 119, 7863–7875

Byrne, M., and P. O'Gorman, 2016: J.Climate. doi:10.1175/JCLI-D-16-0351

LAND-OCEAN DIFFERENCES

Van der Ent et al. (2010): Water Resources Research. Vol 46, W09525

Brubaker et al. (1993): Journal of Climate. 6: 1078

Bosilovich et al. (2005): Journal of Climate. 18: 1591

RECYCLING PROCESSES

OBJECTIVES

• TO DETERMINE SPATIAL AND SEASONAL PATTERNS OF RELATIVE HUMIDITY TRENDS

• TO IDENTIFY POSSIBLE DRIVERS OF RELATIVE HUMIDITY TRENDS:

CLIMATE TRENDS

CHANGES IN EVAPORATION IN OCEANIC HUMIDITY SOURCES

CHANGES IN EVAPOTRANSPIRATION IN CONTINENTAL HUMIDITY SOURCES

Station data: Relativehumidity(3462 stations)

0.5º Gridded Relativehumidity

RELATIVE HUMIDITY TRENDS (1979-2014)

Boreal cold season

-15 -10 -5 0 5 10 15

Rela

tive f

requency

0

2

4

6

8

10

12

14

16

18

0

10

20

30

40

50

Boreal warm season

-15 -10 -5 0 5 10 15

Rela

tive f

requency

0

2

4

6

8

10

12

14

16

0

10

20

30

40

50

Annual

-15 -10 -5 0 5 10 15

Rela

tive f

requency

0

2

4

6

8

10

12

14

16

18

20

0

10

20

30

40

50

HadISDH

Boreal cold season

-15 -10 -5 0 5 10 15

Rela

tive f

requency

0

2

4

6

8

10

12

14

0

10

20

30

40

50

Boreal warm season

-15 -10 -5 0 5 10 15

Rela

tive f

requency

0

2

4

6

8

10

12

0

10

20

30

40

50

Annual

-15 -10 -5 0 5 10 15R

ela

tive f

requency

0

2

4

6

8

10

12

14

16

0

10

20

30

40

50

ERA-Interim

Chi square Sig. C. Contingency

Boreal cold season 915.96 0.000 0.485

Boreal warm season 786.356 0.000 0.46

Annual 1080.115 0.000 0.516

0.5º Land Evapotranspiration

0.5º Ocean Evaporation

0.5º Precipitation and temperature

5º SST

LA PLATA

LA PLATA

LA PLATA: OBSERVED SERIES

LA PLATA: DETRENDED SERIES

WEST SAHEL

WEST SAHEL

WEST SAHEL: OBSERVED SERIES

WEST SAHEL: DETRENDED SERIES

INDIA

INDIA

INDIA: OBSERVED SERIES

INDIA: DETRENDED SERIES

Precipitation

Change in precipitation (%)

-30 -20 -10 0 10 20 30

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = 0.18

p > 0.05

ratio Air Temp./SST

Change in ratio Air Temp./SST

-0.03 0.00 0.03 0.06 0.09 0.12 0.15

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = 0.04

p > 0.05

Ocean Evaporation

Change in Ocean Evaporation (%)

-5 0 5 10 15 20 25

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = -0.13

p > 0.05

Land Evaporation

Change in Land Evaporation (%)

-15 -10 -5 0 5 10 15 20 25

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = 0.47

p < 0.05

Ratio Ocean/Land evaporation(Flexpart)

Change in Ratio Ocean/Land Evaporation (%)

-30 -20 -10 0 10 20

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = -0.03

p > 0.05

Ratio Ocean/Land evaporation(Oaflux/Gleam)

Change in Ratio Ocean/Land Evaporation (%)

-20 -15 -10 -5 0 5 10 15 20C

han

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = -0.46

p < 0.05

A GLOBAL SUMMARY: WARM SEASON

Precipitation

Change in precipitation (%)

-40 -30 -20 -10 0 10 20 30 40

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = 0.47

p < 0.05

ratio Air Temp./SST

Change in ratio Air Temp./SST

0.00 0.03 0.06 0.09 0.12 0.15 0.18 0.21

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = 0.46

p < 0.05

Ocean Evaporation

Change in Ocean Evaporation (%)

0 2 4 6 8 10 12 14 16

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = 0.21

p > 0.05

Land Evaporation

Change in Land Evaporation (%)

-20 0 20 40 60 80

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

8

Pearson's r = 0.62

p < 0.05

Ratio Ocean/Land evaporation(Flexpart)

Change in Ratio Ocean/Land Evaporation (%)

-25 -20 -15 -10 -5 0 5 10 15

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = -0.59

p < 0.05

Ratio Ocean/Land evaporation(Oaflux/Gleam)

Change in Ratio Ocean/Land Evaporation (%)

-40 -30 -20 -10 0 10 20 30C

han

ge i

n R

ela

tive H

um

idit

y-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = -0.66

p < 0.05

A GLOBAL SUMMARY: COLD SEASON

Precipitation

Change in precipitation (%)

-30 -20 -10 0 10 20 30

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = 0.31

p > 0.05

ratio Air Temp./SST

Change in ratio Air Temp./SST

0.00 0.03 0.06 0.09 0.12 0.15 0.18C

han

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = 0.34

p > 0.05

Ocean Evaporation

Change in Ocean Evaporation (%)

0 5 10 15 20 25

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = 0.08

p > 0.05

Land Evaporation

Change in Land Evaporation (%)

-15 -10 -5 0 5 10 15 20 25

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = 0.64

p < 0.05

Ratio Ocean/Land evaporation(Flexpart)

Change in Ratio Ocean/Land Evaporation (%)

-20 -15 -10 -5 0 5 10

Ch

an

ge i

n R

ela

tive H

um

idit

y

-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = -0.4

p > 0.05

Ratio Ocean/Land evaporation(Oaflux/Gleam)

Change in Ratio Ocean/Land Evaporation (%)

-20 -15 -10 -5 0 5 10 15 20

Ch

an

ge i

n R

ela

tive H

um

idit

y-12

-10

-8

-6

-4

-2

0

2

4

6

Pearson's r = -0.55

p < 0.05

A GLOBAL SUMMARY: ANNUAL

Mean = 45 mm/36 years

Mean = 12.4 mm/35 years

Of this precipitation, approximately two thirds is recycled over the continents.

Gimeno et al. (2013): Reviews of Geophysics, 50.

Most of the water that evaporates from the oceans (90%) is precipitated back into them. Only 10% falls as precipitation over the continents.

CORRELATION BETWEEN ANNUAL RH AND LAND EVAPORATION

Evaporation

Negative (p < 0.05)

Negative (p > 0.05)

Positive (p > 0.05)

Positive (p < 0.05)

Magnitude of change in Land Evaporation

Magnitude of change in Relative Humidity

CONCLUSIONS

• HIGH SPATIAL VARIABILITY IN RELATIVE HUMIDITY TRENDS BETWEEN1979 AND 2014

• GOOD AGREEMENT BETWEEN OBSERVATIONS AND ERA-INTERIM DATA

• HIGH SPATIAL VARIABILITY IN THE INFLUENCE OF PRECIPITATION, LANDEVAPOTRANSPIRATION AND OCEAN EVAPORATION ON RELATIVEHUMIDITY TRENDS

• LAND EVAPOTRANSPIRATION VARIABILITY SEEMS TO BE THE MAINDRIVERS OF RELATIVE HUMIDITY TRENDS AT THE GLOBAL SCALEALTHOUGH THERE ARE STRONG SPATIAL DIFFERENCES AND IN SOMEAREAS OF THE WORLD THE INFLUENCE IS NOT CLEAR.