LONGTERM TALL TOWER CO 2 MONITORING IN HUNGARY

LONG-TERM TALL TOWER CO 2 MONITORING IN HUNGARY László HASZPRA Hungarian Meteorological Service Zoltán BARCZA Eötvös Loránd University

Hegyhátsál is located at 46° 57'N, 16° 39'E, 248 m above the sea level 15 OE 48 ON 47 ON 46 ON 16 OE 17 OE 18 OE 19 OE

– 1993 weekly NOAA flask sampling at 96 m – 1994 CO 2 vertical profile measurements (10 m, 48 m, 82 m, 115 m) – 1997 CO 2 vertical flux measurements (eddy covariance method, 82 m) Q 2001 regular aircraft measurements over the tower up to 3000 m above ground

Early afternoon parallel in-situ measurements and flask samples (NOAA) can be used for quality control The slight deviation can be explained by the relatively high temporal variability, the non-perfect synchronization of the insitu measurements and the flask sampling and by the difference in the sampling elevations

black line = marine boundary layer (mbl) Combined data series of the two Hungarian CO 2 monitoring stations K-puszta (KPU, 46º 58'N, 19º 33'E, 125 m, 1981 -1999) and Hegyhátsál (HHS, 46º 57'N, 16º 39'E, 248 m, 1994 - )

Detrended data series Annual amplitude is decreasing (36. 5 ppm → 28. 7 ppm, 0. 78 ppm/yr) Change is not symmetric

CO 2 deficit season Changing shape of the seasonal cycle Increase of the length of the CO 2 deficit season is approx. 1 day/year Increasing length of the growing season?

Possible reasons for the decreasing annual amplitude: • decreasing anthropogenic emission • in Hungary and in the neighbouring countries anthropogenic CO 2 emission hardly changed between 1994 and 2004 • decreasing atmospheric stability, circulation • no sign of significant changes • decreasing biospheric uptake

winter: 1. 91 ppm/yr autumn: 1. 78 ppm/yr annual: 1. 85 ppm/yr spring: 1. 53 ppm/yr summer: 2. 17 ppm/yr mbl: 1. 82 ppm/yr lower than average increase in spring (Mar-May), higher than average increase in summer (Jun-Aug) sign of earlier start of the growing season or more intensive biospheric uptake in spring sign of decreasing summer biospheric uptake

slightly increasing carbon uptake in March → earlier start of the growing season no change in April decreasing carbon uptake from May to August (especially in late summer [July-August]) daytime (08 -16 h LST) NEE

700 600 1960 -1990 average 500 16 1960 -1990 average 50 NEE (g 0 -50 -100 -150 12 no measurements 100 14 March – October temperature (o. C) 400 C/m 2/yr) vapour pressure deficit may give higher correlation March - October precipitation (mm) 800 Haszpra et al. , 2005: Long term tall tower carbon dioxide flux monitoring over an area of mixed vegetation. Agricultural and Forest Meteorology 132, 58 -77.

Conclusions: • in addition to the results of other methods the changes in the temporal variation of CO 2 mixing ratio and the early spring trend in the biosphere-atmosphere carbon exchange rate also indicate the earlier start of the growing season • the gradually drier and warmer than average weather in the growing season resulted in decreasing biospheric carbon uptake between the late 90’s and 2003, turning the region to net carbon source by 2003 • this climate anomaly period seemed to be interrupted in the influence region of the station in 2004, and the region acted again as a net carbon sink • the measurements give the experimental evidence that the expected drier and warmer future climate may turn the region into a significant net natural carbon source