Rainfall Patterns across Puerto Rico: The 1980-2013 Rate of Change Odalys Martínez-Sánchez Lead Forecaster and Climate Team Leader WFO San Juan UPRRP Environmental Sciences PhD Student
Introduction Ways to Analyze Climate Change Time Series : Explains variability of climate data on daily, monthly and seasonal scales. Time series allows you to understand intraseasonal and interannual variability. Frequency Analysis : Explains distribution of climate values. Rate of Change (ROC) : How variables are responding (increase/decrease/no change). How fast the changes occur.
Objective: To determine the 1980 2013 rate of change in seasonal rainfall using the Exponentially Weighted Moving Average (EWMA) and Climate Prediction Center Optimum Climate Normals (CPC OCN).
Methodology Rate of Change (ROC) ROC explains speed of change. The higher the value of ROC, the faster the change occurs; positive/negative values indicate increased/decreased rainfall. It is calculated using the linear slope of the ensemble mean between Climate Prediction Center Optimum Climate Normals and Exponentially Weighted Moving Average. Climate Prediction Center Optimum Climate Normals (CPC OCN) Simple moving average of 15 years which are plotted at the center point of the 15-year period. Since no values are available for the first and last 7 years of the time series, these values are replaced with the first and last available moving average. CPC OCN provides the most recent data average; however, this average cannot be interpreted as the expected or most likely values during the climate change conditions. Exponentially Weighted Moving Average (EWMA) Variation on a moving average method and applies greater weight on the most recent 15-year running mean. EWMA ordinates are plotted at the center point of the 15-year period. The first/last 7 years of the time series are replaced with the first/last available EWMA values as a constant. EWMA provides a more accurate estimate; however, this average still cannot be interpreted as the expected or most likely value during the climate change conditions.
Methodology Continuous data record Period of record must be at least 30 years long. Missing values - Less than 9 days per month (NCDC threshold) (30% of missing values). For this study, selected stations have less than 5 % of missing values. Reliable sources Data well documented (metadata). If a station was relocated, should be compatible (NWS thresholds, within 5 miles and/or 100 feet or less in elevation). For this study, four stations were relocated within 2 miles. Quality controlled data Missing values are filled-in using an optimal interpolation technique.
Methodology Based on the bimodal rainfall pattern, seasons were defined as: Dry Season Dec-Jan-Feb-Mar Rainy Season / 1 st Peak or Initial Maximum Apr-May Relative Minimum / Summer Jun-Jul-Aug Rainy Season / 2 nd Peak Sept-Oct-Nov
Rainfall Pattern and Selected Stations
Rainfall Pattern and Selected Stations In most parts of the Caribbean, rainfall is bimodal with an initial maximum around May, a relative minimum between Jun-Aug (Mid Summer Drought), and a 2nd peak in Sep-Nov. (Rudloff,1981; Giannini et al., 2000; Chen and Taylor, 2002)
RESULTS
San Juan Intl Airport Dry Season Summer 0.077 Inches per year 0.77 Inches per decade 2.31 Inches per 30-year period 0.305 Inches per year 3.05 Inches per decade 9.15 Inches per 30-year period 1980-2010 / without extreme values 0.20 Inches per year 2 Inches per decade 6 Inches per 30-year period
San Juan Intl Airport 1 st Peak 2 nd Peak 0.068 Inches per year 0.68 Inches per decade 2.04 Inches per 30-year period 0.137 Inches per year 1.37 Inches per decade 4.11 Inches per 30-year period
Values in bold indicate the two highest values of ROC per station. Values in blue/brown show an increasing/decreasing trend. *1980-2010 / without extreme values. Decreasing trend. The 1980 2013 Rainfall Rate of Change San Juan Airport Juncos 1SE Guayama 2S Ponce 4E Dry Season 0.077 in/year 0.77 in/ decade 2.31in/30-year period 0.030 in/year 0.3 in/decade 0.9 in/30-year period 0.071 in/year 0.71 in/decade 2.13 in/30-year period 0.036 in/year 0.36 in/decade 1.08 in/30-year period Rainy Season 1 st Peak or Initial Maximum 0.068 in/year 0.68 in/decade 2.04 in/30-year period 0.110 in/year 1.1 in/decade 3.3 in/30-year period 0.119 in/year 1.19 in/decade 3.57 in/30-year period 0.016 in/year 0.16 in/decade 0.48 in/30-year period Summer 0.20 in/year * 2 in/decade* 6 in/ 30-year period* 0.063 in/year* 0.63 in/decade * 1.89 in/30-year period * 0.308 in/year * 3.08 in/decade * 9.24 in/30-year period* 0.104 in/year 1.04 in/decade 3.12 in/30-year period Rainy Season 2nd Peak 0.137 in/year 1.37 in/ decade 4.11 in/30-year period 0.114 in/year 1.14 in/decade 3.42 in/30-year period 0.168 in/year 1.68 in/decade 5.04 in/30-year period 0.103 in/year 1.03 in/decade 3.09 in/30-year period Lajas AES 0.034 in/year 0.34 in/decade 1.02 in/30-year period 0.032 in/year 0.32 in/decade 0.96 in/30-year period 0.033 in/year 0.33in/decade 0.99 in/30-year period 0.015 in/year 0.15 in/decade 0.45 in/30-year period Manati 2E 0.169 in/ year 1.69 in/decade 5.07 in/30-year period 0.022 in/year 0.22 in/decade 0.66 in/30-year period 0.244 in/year 2.44 in/decade 7.32 in/30-year period 0.121 in/year 1.21 in/decade 3.63 in/ 30-year period Adjuntas AES 0.092 in/year 0.92 in/decade 2.76 in/30-year period 0.094 in/year 0.94 in/decade 2.82 in/30-year period 0.074 in/year 0.74 in/decade 2.22 in/30-year period 0.180 Inches per year 1.8 Inches per decade 5.4 in/30-year period Coloso 0.043 in/year 0.43 in/decade 1.29 in/30-year period 0.093 in/year 0.93 in/decade 2.79 in/30-year period 0.166 in/year 1.66 in/decade 4.98 in/30-year period 0.010 in/year 0.1 in/decade 0.3 in/30-year period Data suggest that the faster changes are occurring across most of the stations during Jun thru Nov toward a slightly wetter pattern. A slight decrease in rainfall is also noted across south and southwest PR.
Average Number of Days with rainfall totals 1.5, 2.0 and 3.0 inches. The chance for days with rainfall totals 1.5, 2.0 and 3.0 inches are higher during the 2 nd peak of the rainy season. This maximum is associated with the peak of hurricane season as well as a longer season (1 st peak vs 2 nd peak). Island wide average With just 40% of current decade, 2010-2013 numbers may suggest an increase in number of days with rainfall totals 1.5, 2.0 and 3.0 inches (all season). Summer
Average Number of Days with rainfall totals 1.5, 2.0 and 3.0 inches. Island wide average Average number of days increased in Sep-Oct and Nov during the 2000-2009 decade. No major variation per decade is noted during the dry season as well as the mid summer drought season (without 2010-2013). The average number of days is highly variable during the 1 st peak of rainy season or initial maximum. Summer
Average Number of Days with rainfall totals 1.5, 2.0 and 3.0 inches. Although between 2000 and 2009 the only direct hit was TS Jeanne during Sep 2004, several tropical cyclones left significant rainfall accumulations across Puerto. Erika (Sep. 2009) Hanna (Aug.-Sep. 2008) Jeanne (Sep. 2004) Kyle (Sep. 2008) Mindy (Oct. 2003) Noel (Oct. 2007) Odette (Dec. 2003) Olga (Dec. 2007) T.D. #9A (Aug. 2003) Gaston (Sep. 2010) Otto (Oct. 2010) Therefore, the increase in number of days cannot be associated completely with an increase in shower intensity per se. Distant tropical systems still produce significant rainfall accumulation across Puerto Rico.
Historic Rainfall at San Juan Puerto Rico Tropical wave, divergence aloft, and very high moisture. Streaming effect enhanced instability downwind from the Luquillo Mountain Range and the Cayey Mountain Range. Streamers repeatedly developed producing thunderstorms across San Juan Metro. Rainfall events like July 18, 2013 are extremely rare due to the complexity of environmental factors including local topography.
Findings Rate of Change is a good tool in order to understand how variables are responding. However these values cannot be interpreted as the expected value. Data suggest that the faster changes are occurring across most of the stations during June thru November toward a slightly wetter pattern (around 2 inches per decade during the mid summer drought and 1.50 inches per decade during the 2nd peak of rainy season). A slight decrease in rainfall is also noted across portions of south and southwest PR. The average number of days with rainfall totals 1.5, 2.0 and 3.0 inches increased in Sep-Oct and Nov during the 2000-2009 decade. This increase cannot be associated completely with an increase in shower intensity per se. Distant tropical systems still produce significant rainfall accumulation across Puerto Rico. With just 40% of current decade, 2010-2013 numbers may suggest an increase in number of days with rainfall totals 1.5, 2.0 and 3.0 inches (all seasons). Rainfall events like July 18, 2013 are extremely rare due to the complexity of environmental factors including local topography. Further analysis is required, especially to include NAO and ENSO influences.
National Climate Assessment Observed and Projected Climate Change Daily and five-day rainfall intensities have increased. (unclear, however 2010-2013 numbers may suggest an increase, finding #2). Summers have been either increasingly dry or extremely wet. (finding #1, toward a slightly wetter pattern) For the Caribbean, rainfall trends are unclear, with some regions experiencing smaller annual amounts of rainfall and some increasing amounts. (finding #1) For the Caribbean, is difficult to project the magnitude of rainfall changes, although the majority of models show future decreases in precipitation are likely. In general, annual average decreases are likely to be spread across the entire region.
THANKS FOR YOUR ATTENTION
ADDITIONAL INFORMATION
Dry Season Coloso Summer 0.043 Inches per year 0.43 Inches per decade 1.29 Inches per 30-year period 0.166 Inches per year 1.66 Inches per decade 4.98 Inches per 30-year period
Coloso 1 st Peak 2 nd Peak 0.093 Inches per year 0.93 Inches per decade 2.79 Inches per 30-year period 0.010 Inches per year 0.1 Inches per decade 0.3 Inches per 30-year period
Dry Season Ponce 4 E Summer 0.036 Inches per year 0.36 Inches per decade 1.08 Inches per 30-year period 0.104 Inches per year 1.04 Inches per decade 3.12 Inches per 30-year period
Ponce 4 E 1 st Peak 2 nd Peak -0.016 Inches per year -0.16 Inches per decade -0.48 Inches per 30-year period 0.103 Inches per year 1.03 Inches per decade 3.09 Inches per 30-year period
Dry Season Juncos 1 SE Summer 0.030 Inches per year 0.3 Inches per decade 0.9 Inches per 30-year period 0.166 Inches per year 1.66 Inches per decade 4.98 Inches per 30-year period 1980-2010 / without extreme values 0.063 Inches per year 0.63 Inches per decade 1.89 Inches per 30-year period
Juncos 1 SE 1 st Peak 2 nd Peak 0.110 Inches per year 1.1 Inches per decade 3.3 Inches per 30-year period 0.114 Inches per year 1.14 Inches per decade 3.42 Inches per 30-year period
Dry Season Guayama 2 E Summer 0.071 Inches per year 0.71 Inches per decade 2.13 Inches per 30-year period 0.359 Inches per year 3.59 Inches per decade 10.77 Inches per 30-year period 1980-2010 / without extremes values 0.308 Inches per year 3.08 Inches per decade 9.24 Inches per 30-year period
Guayama 2 E 1 st Peak 2 nd Peak 0.119 Inches per year 1.19 Inches per decade 3.57 Inches per 30-year period 0.168 Inches per year 1.68 Inches per decade 5.04 Inches per 30-year period
Dry Season Lajas AES Summer -0.034 Inches per year -0.34 Inches per decade -1.02 Inches per 30-year period 0.033 Inches per year 0.33 Inches per decade 0.99 Inches per 30-year period
Lajas AES 1 st Peak 2 nd Peak 0.032 Inches per year 0.32 Inches per decade 0.96 Inches per 30-year period -0.015 Inches per year -0.15 Inches per decade -0.45 Inches per 30-year period
Dry Season Manati 2 E Summer 0.169 Inches per year 1.69 Inches per decade 5.07 Inches per 30-year period 0.244 Inches per year 2.44 Inches per decade 7.32 Inches per 30-year period
Manati 2 E 1 st Peak 2 nd Peak 0.022 Inches per year 0.22 Inches per decade 0.66 Inches per 30-year period 0.121 Inches per year 1.21 Inches per decade 3.63 Inches per 30-year period
Dry Season Adjuntas AES Summer 0.092 Inches per year 0.92 Inches per decade 2.76 Inches per 30-year period 0.074 Inches per year 0.74 Inches per decade 2.22 Inches per 30-year period
Adjuntas AES 1 st Peak 2 nd Peak 0.094 Inches per year 0.94 Inches per decade 2.82 Inches per 30-year period 0.180 Inches per year 1.8 Inches per decade 5.4 Inches per 30-year period
1967 44.31 1994 46.79 1995 46.79 1997 49.52 1976 49.91 1991 50.50 1957 53.49 1973 54.93 2000 58.03 1953 58.34 1960 103.73 2011 94.32 1963 90.21 1979 88.91 1961 88.35 2003 87.77 1970 87.38 1998 85.26 2005 83.37 2010 83.33
Summary ENSO-neutral conditions continue.* ENSO Alert System Status: El Niño Watch Positive equatorial sea surface temperature (SST) anomalies continue across most of the Pacific Ocean. The chance of El Niño is at 60-65% during the Northern Hemisphere fall and winter.*
NOAA Operational Definitions for El Niño and La Niña El Niño: characterized by a positive ONI greater than or equal to +0.5ºC. La Niña: characterized by a negative ONI less than or equal to -0.5ºC. By historical standards, to be classified as a full-fledged El Niño or La Niña episode, these thresholds must be exceeded for a period of at least 5 consecutive overlapping 3-month seasons. CPC considers El Niño or La Niña conditions to occur when the monthly Niño3.4 OISST departures meet or exceed +/- 0.5 C along with consistent atmospheric features. These anomalies must also be forecasted to persist for 3 consecutive months.
Historical El Niño and La Niña Episodes Based on the ONI El Niño Highest ONI Value La Niña Lowest ONI Value JJA 1951 DJF 1951/52 1.2 DJF 1952/53 JFM 1954 0.8 MAM 1957 JJA 1958 1.8 OND 1958 FMA 1959 0.6 MJJ 1963 JFM 1964 1.4 AMJ 1965 MAM 1966 1.9 JAS 1968 DJF 1969/70 1.1 AMJ 1972 FMA 1973 2.1 ASO 1976 - JFM 1977 0.8 ASO 1977 JFM 1978 0.8 AMJ 1982 MJJ 1983 2.2 JAS 1986 JFM 1988 1.6 AMJ 1991 MJJ 1992 1.6 ASO 1994 FMA 1995 1.2 AMJ 1997 MAM 1998 2.4 AMJ 2002 JFM 2003 1.3 JJA 2004 DJF 2004/05 0.7 ASO 2006 DJF 2006/07 1.0 JJA 2009 MAM 2010 1.6 ASO 1949 JAS 1950-1.4 SON 1950 JFM 1951-0.8 AMJ 1954 NDJ 1956/57-1.7 AMJ 1964 DJF 1964/65-0.8 JJA 1970 DJF 1971/72-1.3 AMJ 1973 JJA 1974-2.0 SON 1974 MAM 1976-1.7 ASO 1983 DJF 1983/84-0.9 SON 1984 ASO 1985-1.1 AMJ 1988 AMJ 1989-1.9 ASO 1995 FMA 1996-0.9 JJA 1998 FMA 2001-1.7 OND 2005 FMA 2006-0.9 JAS 2007 MJJ 2008-1.5 OND 2008 FMA 2009-0.8 JJA 2010 MAM 2011-1.5 ASO 2011 FMA 2012-1.0
Historical El Niño and La Niña Episodes Based on the ONI Year DJF JFM FMA MAM AMJ MJJ JJA JAS ASO SON OND NDJ 2002-0.2 0.0 0.1 0.3 0.5 0.7 0.8 0.8 0.9 1.2 1.3 1.3 2003 1.1 0.8 0.4 0.0-0.2-0.1 0.2 0.4 0.4 0.4 0.4 0.3 2004 0.3 0.2 0.1 0.1 0.2 0.3 0.5 0.7 0.8 0.7 0.7 0.7 2005 0.6 0.4 0.3 0.3 0.3 0.3 0.2 0.1 0.0-0.2-0.5-0.8 2006-0.9-0.7-0.5-0.3 0.0 0.1 0.2 0.3 0.5 0.8 1.0 1.0 2007 0.7 0.3-0.1-0.2-0.3-0.3-0.4-0.6-0.8-1.1-1.2-1.4 2008-1.5-1.5-1.2-0.9-0.7-0.5-0.3-0.2-0.1-0.2-0.5-0.7 2009-0.8-0.7-0.5-0.2 0.2 0.4 0.5 0.6 0.8 1.1 1.4 1.6 2010 1.6 1.3 1.0 0.6 0.1-0.4-0.9-1.2-1.4-1.5-1.5-1.5 2011-1.4-1.2-0.9-0.6-0.3-0.2-0.2-0.4-0.6-0.8-1.0-1.0 2012-0.9-0.6-0.5-0.3-0.2 0.0 0.1 0.4 0.5 0.6 0.2-0.3 2013-0.6-0.6-0.4-0.2-0.2-0.3-0.3-0.3-0.3-0.2-0.3-0.4 2014-0.6-0.6-0.5-0.1 0.1 0.1 0.0