The
following graphic shows the mean level of Trasimeno Lake during
last 18 years. It plots monthly avarage values got from San
savino hydrometer (more axact than Isola Polvese hydrometer).
The program considered right values that ones with difference
less than 3 cm from the 10 previous values and the 10 next
values (10 acquisitions represent 5 hours since the stations
acquire data every 30 minutes), we suppose impossible this
height variation in such short time. In this way we deleted many
errors due to the natural waves, boat waves and other not
expected phenomenon. It is evident on the graphic how since 1989
the level was always above the hydrometric zero and in spite of
the seasonal periodic trend (usually with minimum during
September/October and maximum during February/March), the global
trend always was negative until 2003. Just last 3 years the
trend changed.
On
these graphics you can see the extreme values of annual levels of
Trasimeno Lake in comparison with the mean annual level and the
hydrometric zero. In the same way as the previous graphic here you
can see the trend changed last 3 years. The minimum value was -187
cm (255.46
m slm) between
15th
and 20th
October 2003,
the minimum mean
annual value was in
2004 with
-150.6
cm.
Minimum
values
[cm] 1988-2005: -3 -27 -80 -85 -66 -83 -86 -110 -130 -114 -97 -108
-114 -114 -142 -187 -174 -144
Maximum
values
[cm] 1988-2005: 56 18 -11 -32 -17 -23 -28 -50 -83 -57 -41 -55 -46
-41 -100 -100 -124 -63
Mean
values
[cm] 1988-2005: 25.4 -11 -43.5 -53 -36.2 -43.7 -57.9 -81.5 -101.8
-77.8 -67.2 -79.1 -78.8 -76 -120.6 -140.2 -150.6 -114.4
On
this graphic we show the cumulated rain for all the weather
stations of Trasimeno basin and the mean value of the basin.
Please
note:
-
La Cima weather station (not so far from the lake coast, but with
really different elevation) usually acquired bigger amount of rain
than the other stations
-
Years 2002 and 2003, were very dry and you can note the
correlation between the minimum amount of rain and the minimum
hydrometric level in the same period
